MOSCOW — Combined Russian-separatist forces in eastern Ukraine claimed Wednesday to have seized control of a frontline town in government-controlled territory, threatening to reignite the bloody, 14-month-long war that has claimed over 6,400 lives.

Ukrainian military spokesman Andriy Lysenko said rebels had mounted an artillery attack against the government-held suburbs of Marinka and Krasnohorivka to the west of the separatist stronghold of Donetsk early Wednesday morning, closing roads and checkpoints to and from the area. Yury Biryukov, a presidential advisor, said two Ukrainian servicemen had died, and 30 more were wounded in the battle near Marinka.

"The enemy is trying to advance. Ukrainian troops are repelling all attacks, and successfully holding on to their positions," Lysenko said.

Eduard Basurin, a military spokesman for the rebels in Donetsk, said at least 15 of their fighters had been killed. The fighting also cut off electricity at the Zasyadko mine, leaving 576 miners underground without light. Meanwhile at the nearby Skochinsky mine, a power outage caused by shelling trapped over 350 people, according to the separatists' information site. Emergency services in the separatist-controlled region of Donetsk had been dispatched to evacuate workers at Skochinsky.

Rebel leaders in previous days have sworn to recapture land lost to them during a Ukrainian advance last summer.

The Armed Forces of Ukraine said 1,000 rebels with at least 10 tanks and other self-propelled artillery, and denied reports that they had lost their positions around the town.

Photographs and videos published online by residents in the area appeared to show thick, black columns of smoke rising above the districts where Ukrainian authorities said fighting was taking place.

To counter the rebels' attack, Ukraine's General Staff said it was bringing back withdrawn artillery to the front lines near Marinka. The ceasefire agreed in February had required the warring parties to withdraw their heavy artillery, including tanks and multiple-launch rocket systems used previously to devastating effect on rural and residential areas alike by both sides.

Basurin said their move was not an offensive one, but a defensive one.

But a post on a rebel website seemed to contradict his statement. "As a result of a massive attack by [Donetsk People's Republic] armed forces, Marinka has been liberated," it said.

Марьинка наша!Только что к нам поступило сообщение от бойца армии ДНР Павла Кухмирова (позыной "Шекспир"), что в резул... Posted by Новости Донецкой Народной Республики on Wednesday, June 3, 2015

The ceasefire has been routinely violated for months. Monitors from the Organization for Security and Cooperation in Europe documented violations by both sides. In its latest report on Monday, the OSCE said there had been 109 mainly outgoing explosions from the area around Donetsk airport, which is under rebel control. That neighborhood is around 10 miles from where fighting took place on Wednesday.

But Wednesday's violence was more reminiscent of the deadly scenes in January and February, when the rebels seized the strategic junction town of Debaltseve.

That surge in violence is worrying, as it comes amid reports of tanks and other artillery trundling through rebel-held towns toward the front lines this week. Russian military forces have also been spotted massing in past days on the border near Ukraine, and the OSCE spotted fighters wearing insignia of the Russian military inside Donetsk.

Ukrainian Prime Minister Arseniy Yatsenyuk, pulling no punches, accused the Kremlin of ordering Wednesday's assault after blowing off peace talks in Minsk on Tuesday.

"Yesterday, Russia broke up the meeting of the trilateral contact group, and today Russia ordered its terrorists to launch a military operation [against Ukraine]," Yatsenyuk was quoted as saying by the Interfax news agency.

Russia has vehemently denied playing a direct role in the conflict, despite a plethora of evidence proving it has supplied manpower and military materiel to the rebels.

But in Moscow, Igor "Strelkov" Girkin, the enigmatic former rebel commander and self-professed ex-colonel in Russia's FSB security service, said: "We [Russia] are conducting special operations there [in Ukraine], but everything is a big secret."

The country has also provided guidance, which is apparently what Vladislav Surkov, a top Kremlin ideologist and foreign policy advisor who has the ear of President Vladimir Putin, was giving to separatist leaders this week in Donetsk.

The Kremlin has not released information regarding his visit, but Strelkov confirmed to Mashable that Surkov had visited Donetsk this week, but was tightlipped about his goings-on there.

Igor Strelkov attends a roundtable to discuss Russia's future in Moscow on June 3, 2015.

In a post attributed to Strelkov on Tuesday, he said Surkov "yelled and swore a lot" at Donetsk rebel leader Alexander Zakharchenko for not following orders like Igor Plotnitsky, his counterpart in neighboring Luhansk region.

Strelkov would like to see the two regions join together under one flag as "Novorossiya," or New Russia, a Czarist-era term used for a large area of southeastern Ukraine. The term was used several times last year by Putin to describe the region. But that hope appears to have been dashed after it was announced last week that the project had closed.

When asked whether Novorossiya had died, Strelkov told Mashable, "Never. It lives."

When told about the fight underway around Marinka, he responded with a resounding "good." And then he sped away in a black SUV.

Just asked Strelkov: Surkov in Donbass? "Can't talk of it. Sorry." But he was there? "Da." Novorossiya dead? "Never." pic.twitter.com/edGhfUYh2L — Christopher Miller (@ChristopherJM) June 3, 2015

Additional reporting by The Associated Press