Story highlights Russia's Putin says talks with Ukrainian President Poroshenko were positive

Poroshenko had said earlier that talks could decide future peace of Europe

Ukraine's Security Service says 10 Russian soldiers were detained in the Donetsk region

Russian state media cites a source saying the soldiers crossed the border accidentally

Ten Russian soldiers were detained in the Donetsk region of eastern Ukraine, that country's Security Service said Tuesday, as tensions simmered over the conflict between Ukrainian forces and pro-Russian rebels.

The Russian soldiers were captured with documents and weapons on them, the Security Service said.

Moscow has repeatedly denied claims by Kiev that it has sent troops and weapons over the border into Ukraine, where the Ukrainian military is fighting pro-Russian rebels.

Russia's state-run RIA Novosti news agency cited a source in the Russian Defense Ministry as saying the soldiers had been patrolling the border and "most likely crossed by accident" at an unmarked point.

The development came as Ukrainian President Petro Poroshenko and his Russian counterpart, Vladimir Putin, met for the first time since June.

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Photos: Photos: Crisis in Ukraine Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels fire artillery Tuesday, October 14, at Donetsk Sergey Prokofiev International Airport, which is on the outskirts of Donetsk, Ukraine. Fighting between Ukrainian troops and pro-Russian rebels in the country has left more than 3,000 people dead since mid-April, according to the United Nations. Hide Caption 1 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke rises behind the train station in Donetsk, Ukraine, during an artillery battle between pro-Russian rebels and Ukrainian government forces on Sunday, October 12. Hide Caption 2 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian President Petro Poroshenko, center, inspects Ukrainian army positions close to Donetsk on Friday, October 10. Hide Caption 3 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – The main terminal of Donetsk Sergey Prokofiev International Airport is hit by shelling during fighting between pro-Russian rebels and Ukrainian forces on Wednesday, October 8. Hide Caption 4 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels fire mortars toward Ukrainian positions near to the Donetsk airport on October 8. Hide Caption 5 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel walks past a burning house after shelling in the town of Donetsk, Ukraine, on Sunday, October 5. Hide Caption 6 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – An Ukrainian sniper aims his weapon at a checkpoint near Popasna, Ukraine, on Thursday, October 2. Hide Caption 7 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke rises from the area near the Donetsk airport after heavy shelling on October 2. Hide Caption 8 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – An injured man is transported at a hospital after shelling in Donetsk on Wednesday, October 1. Hide Caption 9 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A woman injured at a bus station cries at a Donetsk hospital on October 1. Hide Caption 10 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel guards a damaged school in Donetsk on October 1. Hide Caption 11 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian servicemen patrol in the Donetsk region on Friday, September 26. Hide Caption 12 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel guards a destroyed bridge in Nyzhnya Krynka, Ukraine, on Tuesday, September 23. Hide Caption 13 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Residents clean up debris at a building damaged by rockets in Debaltseve, Ukraine, on Monday, September 22. Hide Caption 14 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A firefighter checks out a damaged office building after shelling in Donetsk on Sunday, September 21. Hide Caption 15 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian soldier guards pro-Russian rebels during a prisoner exchange near Donetsk on September 21. Hide Caption 16 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Members of the Ukrainian military, held as prisoners of war, sit in a bus waiting to be exchanged near Donetsk on Saturday, September 20. Hide Caption 17 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke rises after an explosion at a weapons factory controlled by pro-Russian rebels near Donetsk on September 20. The cause of the explosion was not immediately known. Hide Caption 18 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian helicopter patrols an area near Donetsk on September 20. Hide Caption 19 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A firefighter walks past the rubble of a building destroyed by shelling in Donetsk on Wednesday, September 17. Hide Caption 20 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A protester holds a smoke bomb during a demonstration outside the Presidential Palace in Kiev, Ukraine, on September 17. Activists protested the adoption of legislation giving greater autonomy to rebel-held parts of eastern Ukraine's Donetsk and Luhansk regions. Hide Caption 21 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A man covers the body of his mother, who was killed on a bus during a battle in Donetsk on Tuesday, September 16. Hide Caption 22 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – People walk through a market Monday, September 15, in the Kievsky district of Donetsk. Hide Caption 23 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke rises around the Donetsk International Airport on Saturday, September 13, as shelling continues between pro-Russian rebels and the Ukrainian army. Hide Caption 24 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian soldier stands guard as residents rally in support of a united Ukraine in the southern Ukrainian city of Mariupol on September 13. Hide Caption 25 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Russian trucks, flying Russian flags and carrying humanitarian aid for eastern Ukraine, line up at a border checkpoint in Donetsk on September 13. Hide Caption 26 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Workers unload supplies from Russia in Luhansk, Ukraine, on September 13. More than 200 Russian trucks entered Ukraine with supplies for the city, which has been cut off from electricity and water for weeks. Hide Caption 27 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers ride on an armored vehicle near Kramatorsk, Ukraine, on September 13. Hide Caption 28 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – People look at a large crater from a reported missile strike that hit a bus station Friday, September 12, in Makiivka, Ukraine. Hide Caption 29 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Workers clear rubble Thursday, September 11, after the bombing of a mine in Donetsk. Hide Caption 30 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A column of Ukrainian forces is seen in Volnovakha, Ukraine, on September 11. Hide Caption 31 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – An elderly woman sits next to a Ukrainian soldier standing guard in Volnovakha on September 11. Hide Caption 32 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Armed pro-Russian rebels walk September 11 in front of the destroyed Luhansk International Airport. The rebels took control of the airport on September 1 after heavy fighting with the Ukrainian army. Hide Caption 33 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Residents of Lutuhyne, Ukraine, push containers in a wheelbarrow September 11 as they walk between destroyed armored vehicles left behind by the Ukrainian army. Hide Caption 34 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian troops protect themselves from a nearby shooting in Debaltseve on Tuesday, September 9. Hide Caption 35 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Young residents of Berdyansk, Ukraine, dig trenches September 9 to help Ukrainian forces protect the city from possible rebel attacks. Hide Caption 36 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian President Petro Poroshenko, left, inspects military personnel during a visit to Mariupol on Monday, September 8. Hide Caption 37 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel stands next to a truck with a heavy machine gun attached to it Sunday, September 7, in Donetsk. Hide Caption 38 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Homes smolder after being hit by shelling in Donetsk on September 7. Hide Caption 39 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A woman stands next to a road sign September 7 after an overnight bombing attack at an Ukrainian army checkpoint on the outskirts of Mariupol. Hide Caption 40 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian troops stand on a deserted road as they patrol the border area of the Donetsk and Luhansk regions Friday, September 5, near Debaltseve. Hide Caption 41 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A man repairs damage to a building caused by shelling in Donetsk on September 5. Hide Caption 42 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke rises on the outskirts of Mariupol after pro-Russian rebels fired heavy artillery on September 5. Hide Caption 43 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers ride a tank on a road close to where pro-Russian rebels fired heavy artillery outside Mariupol on September 5. Hide Caption 44 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A wounded Ukrainian soldier is helped by a medical team on the outskirts of Mariupol on September 5. Hide Caption 45 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel holds a destroyed weapon in the village of Novokaterynivka, Ukraine, on Thursday, September 4. Hide Caption 46 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Unmarked military vehicles burn on a country road in Berezove, Ukraine, on September 4 after a clash between Ukrainian troops and pro-Russian rebels. For months, Ukrainian government forces have been fighting the rebels near Ukraine's eastern border with Russia. Hide Caption 47 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – People wait by their cars near Berezove on September 4 as rockets hit the road ahead. Hide Caption 48 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel holds a dog, which has a hand grenade attached to its leash, in Donetsk on Wednesday, September 3. Hide Caption 49 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels fire at Ukrainian army positions in Donetsk on September 3. Hide Caption 50 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian military vehicle patrols in the Donetsk region on September 3. Hide Caption 51 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels hold a man near a column of destroyed Ukrainian military vehicles in Novokaterynivka on Tuesday, September 2. Hide Caption 52 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian military truck passes by a serviceman resting in his military camp in Ukraine's Donetsk region on September 2. Hide Caption 53 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A destroyed Ukrainian military vehicle sits abandoned on the side of the road near Novokaterynivka on September 2. Hide Caption 54 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Men clear rubble in Ilovaisk, Ukraine, on Sunday, August 31. Hide Caption 55 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian troops leave the rebel-held town of Starobesheve on Saturday, August 30. Hide Caption 56 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian loyalist fighter from the Azov Battalion stands guard on a hill on the outskirts of Mariupol on August 30. Hide Caption 57 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel listens to the news on a transistor radio in the town of Novoazovsk, Ukraine, on Friday, August 29. Hide Caption 58 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers stop on a roadside as they wait for the start of their march into Mariupol on Wednesday, August 27. Hide Caption 59 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A man opens a box filled with rocket-propelled grenades left by the Ukrainian army in Starobesheve. Hide Caption 60 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel walks through a local market damaged by shelling in Donetsk on Tuesday, August 26. Hide Caption 61 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian servicemen of the volunteer battalion Azov leave for Novoazovsk on August 26. Hide Caption 62 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels escort captured Ukrainian soldiers in a central square in Donetsk on Sunday, August 24. Hide Caption 63 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – People yell as Ukrainian prisoners are paraded through Donetsk in eastern Ukraine on August 24. Hide Caption 64 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel delivers a speech atop a damaged Ukrainian armored personnel carrier in Donetsk on August 24. Hide Caption 65 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – People look at damaged Ukrainian military equipment in Donetsk on August 24. Hide Caption 66 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – The first trucks of a Russian aid convoy roll on the main road to Luhansk in eastern Ukraine on Friday, August 22. The head of Ukraine's security service called the convoy a "direct invasion" under the guise of humanitarian aid since it entered the country without Red Cross monitors. Hide Caption 67 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel holds shrapnel from a rocket after shelling in Donetsk on August 22. Hide Caption 68 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Residents sit in a makeshift bomb shelter during a shelling in Makiivka on Wednesday, August 20. Hide Caption 69 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Dogs play together as a Russian convoy carrying aid supplies stops at a border control point with Ukraine on August 20. Hide Caption 70 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian forces take their position not far from Luhansk on August 20. Hide Caption 71 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Clouds of smoke are on the horizon as Ukrainian forces and pro-Russian rebels clash in Yasynuvata, Ukraine, on Tuesday, August 19. Hide Caption 72 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – An Ukrainian helicopter flies near Kramatorsk on August 19. Hide Caption 73 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers load a missile during fighting with pro-Russian rebels Monday, August 18, near Luhansk. Hide Caption 74 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Boys play at a refugee camp, set up by the Russian Emergencies Ministry, near the Russian-Ukrainian border on August 18. Hide Caption 75 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers carry weapons at a checkpoint near Debaltseve on Saturday, August 16. Hide Caption 76 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels greet each other as they pass near Krasnodon, Ukraine, on August 16. Hide Caption 77 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A fireman tries to extinguish a fire after shelling in Donetsk on August 16. Hide Caption 78 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian border guards patrol near Novoazovsk on Friday, August 15. Hide Caption 79 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Trucks of a Russian humanitarian convoy are parked in a field outside the town of Kamensk-Shakhtinsky, in the Rostov region of Russia about 20 miles from the Ukraine border, on August 15. Ukrainian officials were preparing to inspect the convoy, which was bound for the conflict-torn east. Hide Caption 80 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A truck driver from the convoy jumps out of a trailer on August 15. The Ukrainian government had expressed fears that the convoy was a large-scale effort to smuggle supplies or troops to pro-Russian rebels. Hide Caption 81 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A tank belonging to pro-Russian rebels moves along a street in Donetsk on August 15. Hide Caption 82 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian soldier walks past a line of self-propelled guns as a column of military vehicles prepares to head to the front line near Ilovaisk on Thursday, August 14. Hide Caption 83 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A Ukrainian soldier prepares a mortar at a position near Ilovaisk on August 14. Hide Caption 84 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A man inspects damage at his house after a shelling in Donetsk on August 14. Hide Caption 85 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A convoy of trucks, which Moscow said was carrying relief goods for war-weary civilians, moves from Voronezh, Russia, toward Rostov-on-Don, Russia, on August 14. Hide Caption 86 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Pro-Russian rebels on the outskirts of Donetsk stand at a checkpoint near a bullet-riddled bus on Wednesday, August 13. Hide Caption 87 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel inspects damage after shelling in Donetsk on Thursday, August 7. Hide Caption 88 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Smoke billows from a Ukrainian fighter jet crash near the village of Zhdanivka, Ukraine, on August 7. Hide Caption 89 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Residents of eastern Ukraine cry in a hospital basement being used as a bomb shelter August 7 in Donetsk. Hide Caption 90 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ordnance from a Ukrainian rocket launcher shoots toward a pro-Russian militant position in the Donetsk region on August 7. Hide Caption 91 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Relatives of Ukrainian military member Kyril Andrienko, who died in combat in eastern Ukraine, gather during his funeral in Lviv, Ukraine, on August 7. Hide Caption 92 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Refugees from southeastern Ukraine wait at a refugee camp in Donetsk on Wednesday, August 6. Hide Caption 93 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian rebel adjusts his weapon in Donetsk on August 6. Hide Caption 94 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Men walk past a bomb crater in Donetsk on August 6. Hide Caption 95 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A man steps out of his car as Ukrainian soldiers inspect the vehicle at a checkpoint in Debaltseve on August 6. Hide Caption 96 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian servicemen sit on a bus near Slovyansk, Ukraine, on Tuesday, August 5. Hide Caption 97 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A pro-Russian separatist guards a road as Australian, Malaysian and Dutch investigators prepare to examine the crash site of Malaysia Airlines Flight 17 near the village of Rossipne, Ukraine, on August 5. U.S. and Ukrainian officials allege that a Russian-made missile shot down the plane from rebel-held territory, killing all 298 people on board. Russia and the rebel fighters deny involvement. Hide Caption 98 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Rescue workers carry the body of a woman who was killed during a bomb shelling in Donetsk on August 5. Hide Caption 99 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A boy stands in a hallway of a refugee hostel run by pro-Russian rebels in Donetsk on Monday, August 4. Hide Caption 100 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian servicemen from the Donbass volunteer battalion clean their guns Sunday, August 3, in Popasna, Ukraine. Hide Caption 101 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian soldiers fire shells toward rebel positions near Pervomaysk, Ukraine, on Saturday, August 2. Hide Caption 102 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – Ukrainian troops patrol near the village of Novoselovka on Thursday, July 31. Hide Caption 103 of 104 Photos: Photos: Crisis in Ukraine Crisis in Ukraine – A woman says goodbye to her mother as she flees her home in Shakhtersk, Ukraine, on Tuesday, July 29. See more photos of the crisis from earlier this year Hide Caption 104 of 104

The two Presidents agreed that they need to "renew our dialogue," Putin said, according to a CNN translation.

Putin said the meeting was "positive."

The two leaders are in Minsk, the capital of Belarus, for talks related to the Eurasian Customs Union, a trade bloc made up of Russia, Belarus and Kazakhstan -- with the crisis in Ukraine expected to dominate.

As the talks started, Poroshenko said "the fate of the world and Europe" could be decided in Minsk. "We must jointly find the only right decision. Peace on the continent depends on it," he said, according to his office.

Senior European Union officials, headed by EU foreign policy chief Catherine Ashton, are also in Minsk for the summit.

"The EU is attending to see if discussions can help create momentum for a new political solution to the crisis in Ukraine," said Ashton's spokeswoman, Maja Kocijancic.

Putin told reporters that Russia couldn't be involved in ceasefire talks because those discussions should be between Kiev and separatists in eastern Ukraine. Moscow is willing to assist, he added.

Putin: Military escalation won't solve crisis

Putin was cited by Russian state media as telling fellow leaders that the crisis in Ukraine "cannot be solved through further escalation of the military scenario."

He said Russia was "ready to exchange opinions" on the conflict and urged dialogue to find a peaceful resolution, state news agency ITAR-Tass reported.

Earlier, Poroshenko spoke with Ashton about the situation in his country's east and the detention of the 10 Russian soldiers, his office said.

He urged the world to support Ukraine and its efforts to secure its border with Russia "to prevent cross-border infiltration of weapons, military equipment and mercenaries." This, he said, would swiftly resolve the situation.

The conflict was first sparked last year by a political crisis over whether Ukraine would seek closer ties with Europe or with Russia. The ouster of pro-Moscow President Viktor Yanukovych in February was followed by Russia's annexation of Ukraine's Crimea region in March and a declaration of independence by separatist leaders in the Donetsk and Luhansk regions.

Poroshenko in June signed a landmark EU trade pact, despite opposition from Russia.

On Tuesday, after meeting with Ashton, the President said Ukraine would ratify the Association Agreement with the European Union in September and immediately send the ratification documents to Brussels.

The move "is in no way aimed against anyone," Poroshenko said, according to a statement from his office. "Instead, the agreement will positively affect relations with all our neighbors, especially in the economic sphere. We would like our international partners to accept our decision."

He added that parliamentary elections scheduled for October 26 should not affect the EU agreement. Poroshenko's trip to Belarus comes a day after he dissolved Ukraine's parliament.

However, Putin warned that it would cost Ukraine billions of euros to try to meet EU trade standards and that Russia, Belarus and Kazakhstan would also lose out. Ukrainian imports would no longer be given preferential treatment, he added.

It's not yet been confirmed whether Putin and Poroshenko, who last met briefly during D-Day commemorations in France, will hold bilateral talks while in Minsk.

'I just want to survive'

Meanwhile, fighting continues for control of Luhansk and Donetsk, both strongholds for the rebel fighters.

Ukraine's National Defense and Security Council said Tuesday that militants and the Russian military have become more active in the east and south of Donetsk, as well as along the border, with 29 clashes in the past day.

Rebel fighters continue to cross the border, backed up by the Russian military firing over the border, NDSC spokesman Col. Andriy Lysenko told reporters at a briefing.

Four Ukrainian border guards died and three were injured when two Russian Mi-24 helicopters fired on them, he said.

Russia denies direct or indirect involvement in the fighting and says Ukraine's assault against the rebels is precipitating a humanitarian crisis.

The besieged city of Luhansk has been without water and power for over three weeks, city officials said Sunday. Shelling has caused major damage there and in surrounding villages over past weeks.

Members of the Mahounin family told CNN how they fled their town two days earlier. Intense shelling meant they'd had to spend 24 hours a day in an underground bomb shelter with more than 100 others.

"I don't care what they're fighting for, I just want to survive -- I want my son to survive," said Lilia Mahounin.

Aid convoy

Lavrov told reporters that Russia hopes to send a second humanitarian aid convoy to Ukraine this week to help civilians caught up in the conflict.

Last Friday, a convoy of 227 Russian trucks crossed that country's border into eastern Ukraine without Kiev's authorization, a move condemned by international powers as a violation of Ukraine's sovereignty. Officials in Kiev referred to it as an invasion.

The trucks left a day later, having successfully delivered supplies to Luhansk, Russian authorities said. Ukrainian authorities said they suspected the delivery had been used to bolster rebel forces.

U.N. officials estimate that more than 2,000 people have died and nearly 5,000 have been wounded in eastern Ukraine since mid-April.

German Chancellor Angela Merkel, on a weekend visit to Kiev, promised Ukraine loans worth 500 million euros to help rebuild shattered infrastructure and homes.