KIEV — Ukraine's acting president accused Russia of open aggression on Friday and said Moscow was following a similar scenario to the one before it went to war with Georgia in 2008.

Urging President Vladimir Putin to stop "provocations" in the Ukrainian region of Crimea, Oleksander Turchinov drew a comparison to Russia's intervention in Georgia over the breakaway Akhazia region which has a large ethnic Russian population.

"Russia has sent forces into Crimea ... they are working on scenarios which are fully analogous with Abkhazia, when having initiated a military conflict, they started to annex the territory," he said in televised comments.

U.S. President Barack Obama on Friday expressed concern about reported Russian military movement inside crisis-torn Ukraine and warned of consequences.

"We are now deeply concerned by reports of military movements taken by the Russian Federation inside of Ukraine," he told reporters at the White House.

"Any violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing," he said in a brief appearance.

"The United States will stand with the international community in affirming that there will be costs for any military intervention in Ukraine."

Any Russian military movements in Crimea are in keeping with Moscow's existing arrangement with Ukraine on the deployment of military assets in the former Soviet republic, Russia's U.N. Ambassador Vitaly Churkin said on Friday.

"We are acting within the framework of that agreement," he told reporters after a closed-door meeting of the U.N. Security Council. He did not give any details or comment on specifics of any Russian military deployments on Ukrainian territory.

Ousted Ukrainian President Viktor Yanukovych reappeared in Russia after a week on the run.

Yanukovych said he would continue the struggle for Ukraine's future as tension soared on the Black Sea peninsula of Crimea, the only region with an ethnic Russian majority and last major bastion of resistance to the overthrow of the Moscow-backed leader.

More than 10 Russian military helicopters flew into Ukrainian airspace on Friday over Crimea, Kiev's border guard service said, accusing Russian servicemen of blockading one of its units in the port city of Sevastopol, where part of Moscow's Black Sea fleet is based.

The fleet denied its forces were involved in seizing one of the airports, Interfax news agency reported, while a supporter described the armed group at the other site merely as Crimean militiamen.

Moscow has promised to defend the interests of its citizens in Ukraine. While it has said it will not intervene by force, Russia's rhetoric since the removal of Yanukovych a week ago has echoed the run-up to its invasion of Georgia in 2008.

Ukraine's top security official, Andriy Paruby, said the armed men were taking their orders from the top in Russia. "These are separate groups ... commanded by the Kremlin," Paruby, secretary of the National Security and Defense Council, told a televised briefing in Kiev.

Russia announced war games on Wednesday near the Ukrainian border, involving 150,000 troops on high alert, although U.S. Secretary of State John Kerry said his Russian counterpart, Sergei Lavrov, had told him the exercises were pre-planned.

Ukraine's new rulers have said loans worth $37 billion went missing from state accounts during Yanukovych's three years in power — a jaw-dropping sum even for a population now used to tales of his extravagance and lavish lifestyle, including his opulent residence outside Kiev.

Kiev's new rulers have said any movement by Russian forces beyond the base in Sevastopol would be tantamount to aggression. But they face a major challenge in Crimea which was Russian territory until it was transferred to Ukraine in 1954, during the Soviet era. Separatism there has often flared up at times of tension between Moscow and Kiev.