Reports that Russia has opened a new front in the war in eastern Ukraine Thursday between pro-Russia separatists and the new government of President Petro Poroshenko have led to widespread condemnation.

U.S. President Barack Obama, speaking to reporters in Washington, said Russia’s actions are leaving it isolated from the international community.

Obama said he spoke with German Chancellor Angela Merkel, and both leaders agreed Russia must face consequences for its actions.

"We agree — if there was ever any doubt — that Russia is responsible for the violence in eastern Ukraine," Obama said. "The violence is encouraged by Russia. The separatists are trained by Russia, they are armed by Russia, they are funded by Russia."

"Russia has repeatedly violated the sovereignty and territory of Ukraine," he added.

Pro-Russian separatists walk at a destroyed war memorial on Savur-Mohyla, a hill east of the city of Donetsk on Thursday. (Maxim Shemetov/Reuters) Obama stopped short of calling it an invasion, and said that a military action from the West is not on the table.

Instead, increasing economic sanctions will seek to punish Russia.

"We are not taking military action to solve the Ukrainian problem," Obama said. "What we're doing is to mobilize the international community to apply pressure on Russia."

The president added that he will meet with Poroshenko at the White House in September, his first visit as president and a symbolic display of unity between the U.S. and Ukraine.

Russia has described the Russian citizens fighting with the separatists as volunteers.

NATO officials said at least 1,000 Russian troops had entered Ukraine. NATO produced satellite images to provide what it called additional evidence that Russian combat soldiers, equipped with sophisticated heavy weaponry, are operating inside Ukraine's sovereign territory.

"This is highly sophisticated weaponry that requires well-trained crews, well-trained command and control elements, and it is extremely unlikely that this sort of equipment is used by volunteers," said Nico Tak, director of NATO's Comprehensive Crisis Operations Management Center.

Tak said the satellite images were only "the tip of the iceberg" in terms of the overall scope of Russian troop and weapons movements.

The new southeastern front raised fears that the separatists are seeking to create a land link between Russia and Crimea, which Russia annexed in March.

Canada’s response

A school damaged by shelling in the town of Donetsk, eastern Ukraine is shown Thursday. (Mstislav Chernov/The Associated Press) Speaking to reporters on a conference call from Zagreb, Croatia, Foreign Affairs Minister John Baird called the activity of Russian and Russian-sponsored units in eastern Ukraine "unacceptable, irresponsible and absolutely reckless."

He also said that Russia has been "deeply and shamelessly dishonest" on the diplomatic front.

"While Russian President Putin talked about ceasefires with President Poroshenko in Minsk, his military was busy fighting on Ukrainian soil.

"Russia's credibility was very limited after the dishonesty and deception over Crimea, now it is non-existent," Baird said.

The UN held an emergency Security Council meeting hours after a top Ukrainian official said two columns of Russian tanks and military vehicles fired missiles from Russia at a Ukraine border post, then rolled into the country.

'Russia has to stop lying'

U.S. Ambassador Samantha Power earlier levelled strong words as she relayed events from the past 48 hours, including when Russian troops supposedly accidentally wandered into Ukraine, which she said fit into a "well-established pattern."

"At every step, Russia has come before this council to say everything except the truth," she said.

“Russia has to stop lying and has to stop fuelling this conflict."

This map indicates where recent clashes between pro-Russian separatists and Ukrainian forces occurred. (Reuters) Prior to the meeting, Russian Ambassador to the UN Vitaly Churkin told reporters "You're at a loss," offering no further comment.

Lithuania's UN ambassador, Raimonda Murmokaite, who requested the emergency meeting, tweeted prior to its start: "An invasion is an invasion is an invasion."

Ukrainian president warns against panic

"Russian forces have entered Ukraine," Poroshenko told the country Thursday morning, cancelling a foreign trip and calling an emergency meeting of the country's security council. "Today the president's place is in Kyiv."

Poroshenko urged his citizens to resist giving into panic.

As Poroshenko spoke, the strategic southeastern town of Novoazovsk appeared firmly under the control of separatists and their Russian backers, a new, third front in the war.

Lysenko said the missiles from Russia were fired at Ukrainian positions in the southeast about 11 a.m. local time and an hour and a half later, two columns, including tanks and other fighting vehicles, began an attack. They entered Ukraine from Veselo-Voznesenka and Maximovo in the Rostov region of Russia.

Also Thursday, 15 civilians were killed in shelling in Donetsk, reported Reuters, citing a statement by city administration on its website. The statement described the general situation there as "very tense."