NATO on Saturday released photos that it said showed recent Russian tank movements near the Ukrainian border, one day after the U.S. State Department asserted Russia had sent tanks and heavy weaponry to separatists in Ukraine.
The tanks in the NATO photos were seen on the Russian side of the border, but a NATO officer told VOA that they were likely the same ones that were shown moving within eastern Ukraine in video circulating on the Internet.
"In the context of a counter-insurgency, tanks are significant," said the official said who spoke on condition of anonymity because he was not authorized to speak on the record. He called them a "psychologically significant platform," that could boost the morale of insurgents.
The official said the tanks are difficult to drive, meaning only someone who had training could operate them properly. That means it was unlikely that the separatists are driving them, he said.
The officer told VOA that the convoy was part of a larger group of military vehicles assembled at a staging area near Rostov-on-Don, about 50 miles from the border with Ukraine. Among them were at least 10 T-64 battle tanks - a Russian model that originally was scheduled to be scrapped but has remained operational.
Russia has about 2,000 functional T-64 tanks at its disposal, the officer said.
Moscow has denied that it supplies or directs the separatist forces in Ukraine, and the rebels battling Ukrainian troops say they have acquired their weapons from government stockpiles.
A day earlier, the U.S. State Department asserted Friday that Russia had in fact sent tanks and other heavy weapons to separatists. Photos and video circulating on the Internet showed as many as three tanks crossing the border near the Ukrainian town of Snizhne.
State Department spokeswoman Marie Harf said that a convoy of three T-64 tanks, several rocket launchers, and other military vehicles crossed the border in the last three days. She called the move "unacceptable."
The Ukrainian Army said it had destroyed two of the tanks and several other vehicles in the convoy.
NATO Secretary-General Anders Fogh Rasmussen said Friday that if reports of "pro-Russian armed gangs" acquiring heavy weapons from Russia were confirmed, it would mark "a serious escalation" of the crisis in eastern Ukraine.
Russia, which annexed Ukraine's Crimea peninsula in March, has repeatedly said it would not make further intrusions into Ukrainian territory.
Meanwhile, Ukraine's government said that its security forces regained control of Mariupol, a port city in the Donetsk region that has changed hands several times.
Interior Minister Arsen Avakov said Ukrainian forces raised the country's flag over city hall.
In another development, Russian forces began military exercises Thursday in the Baltic Sea enclave of Kaliningrad. Moscow says the exercises are a response to ongoing NATO maneuvers in European NATO countries near its borders.
Kaliningrad is a tiny Russian territory wedged between NATO member-states Lithuania and Poland.
In Moscow Thursday, Russian President Vladimir Putin marked one of Russia's main holidays, Russia Day, with praise for the annexation of Crimea.
In an address, Putin said the peninsula and its strategic Black Sea port of Sevastopol have come back to their "homeland."
Western governments and the United Nations say Crimea has been occupied by Russian soldiers.
Some information for this report was provided by AP and Reuters.