Ukrainian troops attacked pro-Russia separatists Friday in the southern port of Mariupol, apparently driving them out of buildings they had occupied in the centre of the city.

Mariupol is the second-largest city in the eastern Donetsk region that has declared independence from the government in Kyiv. The key port sits along the main road leading from Russia to the Crimean Peninsula, which Russia annexed in March from Ukraine.

About 100 soldiers emerged triumphant Friday from the previously rebel-occupied buildings, shouting the name of their battalion, Azov, and singing the Ukrainian national anthem. They also destroyed an armoured vehicle and a heavy truck used by the separatists, leaving the vehicles scorched and riddled with large-calibre bullet holes.

Interior Minister Arsen Avakov said four government troops were wounded in what he called a successful operation. Witnesses said they saw troops capture at least four separatist fighters. There was no immediate word of casualties on the rebel side, and Associated Press journalists at the site were blocked from entering the buildings.

Ukraine and the West have accused Moscow of fomenting the unrest in eastern Ukraine and supporting the separatist fighters. Russia, however, has denied sending troops or weapons to Ukraine and has described the Russian citizens fighting with the separatists as volunteers.

Ukraine

Ukrainian troops stand atop of a vehicle as they leave the scene of fighting in Mariupol. Ukrainian forces retook buildings occupied by the rebels in the centre of the town. (Evgeniy Maloletka/Associated Press)

But on Friday, rebel leaders confirmed they now have three tanks and the U.S. State Department officials said it's sure those weapons came from Russia.

"We assess that separatists in eastern Ukraine have acquired heavy weapons and military equipment from Russia, including Russian tanks and multiple rocket launchers," spokeswoman Marie Harf said in a statement.

Harf told a briefing earlier that a convoy of three T-64 tanks, several MB-21 "or Grad" multiple rocket launchers and other military vehicles had crossed from Russia into Ukraine in the last three days. 

Denis Pushilin, a leader of the separatist Donetsk People's Republic, told Russian state television Friday that they have the tanks but it was "improper to ask" where they had gotten them.

"They are in Donetsk and are the minimum that we have to defend the city," he said.

Canada, NATO concerned about tanks

A spokesman for Prime Minister Stephen Harper said in a statement Friday if the tanks came from Russia, the "reckless" actions would threaten peace in the region.

“Canada is deeply concerned by reports that Russian tanks and other military vehicles may have crossed the border into eastern Ukraine. If confirmed, these are reckless actions that threaten regional and global peace," said Jason MacDonald, the director of communications for the Prime Minister's Office in a statement.

MacDonald said Canada condemns "the Putin regime’s ongoing militarism and expansionism" and said the international community must not stand for transgressions of Ukraine's sovereignty and independence.

“Canada is working closely with its NATO partners and urges Russia to complete the withdrawal of its military forces on the border with Ukraine, to stop the flow of weapons and fighters across the border, and to exercise its influence among armed separatists to lay down their weapons and renounce violence. We will never accept Russia’s illegal occupation and seizure of neighbouring territories," he said.

There was no immediate response from Russia on Friday, which is a national holiday in the country.

Poroshenko's peace talks continue

Pushilin repeated the separatists' call for Russia to send peacekeeping troops into eastern Ukraine. Russia has said this could only be done with UN authorization.

Ukrainian President Petro Poroshenko, who took office on June 7, rallied support for his plan to end the fighting in phone calls Thursday with Russian President Vladimir Putin and German Chancellor Angela Merkel.

Poroshenko told Merkel he is willing to negotiate, but not with those he calls terrorists. He said he could offer amnesty only to people who don't have "blood on their hands."

According to his spokesman, Svyatoslav Tsegolko, Poroshenko told Putin it was "unacceptable" that tanks had crossed the border. A Kremlin statement said Poroshenko told Putin about his plan for resolving Ukraine's crisis.

With files from CBC News