KIEV, Ukraine (USA TODAY) – Ukraine's government said Wednesday it will pull its troops from Crimea, where Russian troops and Crimean allies are seizing military bases and officers.

Masked armed men assumed to be Russian military seized Ukraine's naval headquarters in the city of Sevastopol on the Black Sea in Crimea and took away a Ukrainian admiral.

Ukraine's defense minister and deputy prime minister put off a trip to Crimea in what they said was a bid to avert an escalation in hostilities after the self-appointed prime minister in Crimea, Sergei Aksyonov, warned that they "are not welcome," Interfax news agency said.

The hostilities follow a decree by Russian President Vladimir Putin that the former captive of the Soviet Union, Russia's predecessor, is now part of Russia despite warnings from the White House and Europe that Moscow will pay "costs" for a takeover.

U.S. Vice President Joe Biden, in the former Soviet republic of Lithuania, declared that the U.S. was "absolutely committed" to defending its allies.

"Russia cannot escape the fact that the world is changing and rejecting outright their behavior," Biden said, after meeting in Vilnius with Lithuanian President Dalia Grybauskaite and Latvian President Andris Berzins.

Biden announced no new initiative to get Russia to back away.

TIMELINE: Key events in Ukraine

MORE: Putin's move on Crimea bolsters popularity back home

Ukrainian soldiers in the province of Crimea had been left in limbo after the Crimeans voted Sunday to join Russia, a referendum that Ukraine and the West said was unconstitutional. They held onto their bases, which were surrounded by Russian troops and mobs of pro-Russian Crimeans.

A confrontation at one base on Tuesday that left one Ukraine servicemember dead prompted an order from Kiev that the Ukrainians could fire their weapons to protect themselves. That did not happen though in Sevastopol.

Interfax, a Russian media source, said "unknown" troops took over the base and Ukraine's navy commander, Serhiy Hayduk, was arrested and the Russian flag raised over the base.

Russia said the Ukraine government is no longer legitimate because it ousted president Viktor Yanukovych, a Moscow ally, for the shooting of more than 80 protesters in Kiev.

Ukraine said Wednesday it will exit the Russia-dominated Commonwealth of Independent States set up after the collapse of the Soviet Union, the country's security chief said Wednesday. Andriy Parubiy, secretary of the National Security and Defense Council, said Ukraine would hold military exercises going forward with the United States and Britain.

Russians who want to visit Ukraine will be required to get a visa, the ITAR-Tass news agency reported. Citizens of the two countries had been able to travel back and forth without visas since 1991, when Ukraine became an independent country.

Crimea adopts the ruble, now the official currency of the region a day after being annexed by Russia. Duration: 00:56

Many Ukrainians fear that Russia could also now invade Eastern Ukraine in response to parliament's installation of a pro-Western government. Putin's spokesman Dmitry Peskov told the BBC that Russia would not do so, but some here say he may first blackmail the east by hiking the price of energy exports.

'I think that Russia will fight economically outside Crimea," student Dmitri Alexandrovich said in Kharkiv, a Russian-speaking city in eastern Ukraine. '"Then, once the country is on its knees, 1,000 parts will break away and ask to join Russia."

Vice President Biden pledges to support Baltic allies worried by Russian aggression. Leigh Paterson reports. Newslook

Charles McPhedran, Special for USA TODAY; Contributing: Luigi Serenelli, Associated Press

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