SEVASTOPOL, Ukraine — Unidentified armed men who may belong to the Russian military are blockading an airport near Sevastopol Friday in an escalation of tensions between the neighboring states that Ukraine's interior minister is calling an "armed invasion."

"I can only describe this as a military invasion and occupation," Ukraine's new Interior Minister Arsen Avakov wrote in a post on Facebook.

The Russian foreign ministry refused to comment to the Associated Press, but Russia's defense ministry told the Interfax news agency that there had been "no provocative acts in relation to units and divisions" from Russian forces stationed in the region.

Dozens of armed men in military uniforms without markings have also apparently taken over the main airport in Simferopol, the capital of Crimea, although it has not been confirmed that the men at either airport belong to Russian military units. There were also reports that some of the men have started to partially withdraw.

While no violence has so far been reported, any Russian military incursion in Crimea would dramatically raise the stakes in Ukraine's conflict, which saw the pro-Russian president flee last weekend after three months of anti-government protests. Moscow has vowed to protect Russian-speaking Ukrainians in Crimea, where it has a major naval base, and Ukraine and the West have warned Russia to stay away.

"There is an acute need right now to support our families, make them secure, and protect our society," said Andrey Sitnikov in Sevastopol, who says he is there as private citizen.

At Sevastopol's Belbek International Airport on Friday, around 15 to 20 members of a Ukrainian political party called the Russian Bloc representing ethnic Russians set up an informal blockade to support the armed men with their own civilian barricade a hundred meters from the airport. A private car has coffee, tea and sandwiches in its open trunk, free for anyone to take.

A Russian truck with insignias and number plates removed was spotted exiting the Sevastopol airport. Ukrainian local police are present but did not attempt to stop the vehicle.

More checkpoints have been set up in the strongly pro-Russian city scrutinizing all arrivals and Reuters reported that Russian military helicopters have traveled to the Crimea.

The blockade may signal an unwillingness to negotiate with Kiev, said Yaroslav Pylynskyi, director of the Kennan Institute at the Wilson Center, a policy research institute in Kiev.

"I heard the people blocking the airport were trying to prevent people from Kiev coming for negotiations," he said. "The [ethnic Russians in Crimea] did not want negotiations, because they are being controlled by Moscow. I guess they also do not know what to do in that situation."

Responding to the situation on Friday, Ukrainian lawmakers asked the the United Nations' Security Council to address the country's political turmoil.

On Thursday, armed men seized the Crimea parliament as Russian jets streaked near the border and a newly created Ukraine government formed to try to end a crisis that threatens to split the country following the ouster of its president.

After capturing the parliament and government offices in Simferopol the masked men raised the Russian flag over the parliament building.

UKRAINE: Ousted leader Viktor Yanukovych in Russia

Ukraine's ousted President Viktor Yanukovych has a news conference scheduled Friday in Russia's south near the Ukrainian border. After surfacing in Moscow, he declared Thursday in a statement that he remains Ukraine's legitimate president.

Authorities in Switzerland moved to freeze any funds belonging to the former leader or his family and allies.

In a separate development Friday, the National Bank of Ukraine — the nation's central bank — put a $1,500 limit on foreign currency withdrawals in a bid to counter falling values in the hryvnia, Ukraine's currency.

Contributing: Janelle Dumalaon from Berlin

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