MARIUPOL, Ukraine -- Ukrainian troops and pro-Russia separatists clashed Friday in a southern port town, as the United States confirmed earlier reports that a convoy of armored vehicles including three T-64 Russian tanks moved into Ukraine from Russia and now are in the hands of the rebels.

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

Mariupol is the second-largest city in the eastern Donetsk region, where armed separatists have declared independence from the government in Kiev. The Azov Sea port sits along the main road leading from Russia to the Crimean Peninsula, which Russia annexed in March from Ukraine.

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.

The renewed fighting Friday came as State Department officials in Washington confirmed Russia had sent tanks and rocket launchers to the rebels.

U.S. State Department spokeswoman Marie Harf said the U.S. had information that Russia has accumulated tanks of a type no longer used by its own forces at a site in southwest Russia, and some had recently left that spot. Internet videos later showed tanks of the same make moving through several cities in eastern Ukraine.

"In the last three days, a convoy of three T-64 tanks, several BM-21 or Grad multiple rocket launchers and other military vehicles crossed from Russia into Ukraine near the Ukrainian town of Snizhne. This is unacceptable," Harf told reporters in Washington.

She added: "We are confident that these tanks came from Russia."

Also Friday, rebel leaders confirmed they had obtained three tanks.

Denis Pushilin, a leader of the separatist Donetsk People's Republic, told Russian state television Friday that they had 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.

NATO condemned the reports of Russian tanks.

"I am concerned about reports that pro-Russian armed gangs are acquiring heavy weapons from Russia, including Russian tanks," NATO Secretary-General Anders Fogh Rasmussen said in a statement Friday. "This would mark a serious escalation of the crisis in eastern Ukraine."

The U.S. urged Russia to back the peace plan laid out by new Ukrainian President Petro Poroshenko.

Russia has not commented on the tanks, but its border guard service said two Ukrainian armored vehicles crossed the border in the opposite direction Friday, into Russian territory near the southern city of Rostov-on-Don. Russian news agencies quoted a spokesman for the border guard service as saying that the Ukrainian troops were able to return to Ukraine but left behind one of the vehicles.