Russia sent fighter jets to patrol its border with Ukraine on Thursday, as fast-paced developments threatened to undermine the new Ukrainian government in Kyiv.
Gunmen seized control of government buildings in Crimea, a Ukrainian region with strong ties to Moscow and home to a Russian naval base in Sevastpol. The gunmen raised the Russian tri-color flag.
Meanwhile, Russian news agencies reported that Moscow had granted ousted Ukrainian President Viktor Yanukovych's request for personal security "on Russian territory," but provided no other details.
While Russian jets soared through the skies in military exercises ordered by President Vladimir Putin, U.S. Defense Secretary Chuck Hagel warned Moscow to not take any action on Ukraine that could be misinterpreted.
Hagel said the U.S. strongly supports Ukraine's territorial rights and that Russia and all countries should offer "very cool, wise leadership."
In Kyiv, the parliament approved former economic minister Arseny Yatseniuk as the country's new prime minister. He accused the Yanukovych government of stealing vast sums from state coffers, leaving the country in severe financial straits.
Mr. Yatseniuk said $70 billion in Ukrainian government money had been sent to offshore accounts over the last three years and that $37 billion of credit it had received has disappeared.
He said, "I want to report to you. The state treasury has been robbed and is empty."
Mr. Yanukovych released a statement to Russian news agencies from an undisclosed location saying that he still considers himself Ukraine's head of state. He has not been seen in public since Saturday, when Ukraine's parliament voted to dismiss him and set early elections for May 25.
Crimea has been the scene of confrontations between supporters of Ukraine's new government and pro-Russia activists. The region is mainly made up of Russian speakers who support Moscow but is also home to minority Muslim Tatars who are generally anti-Russia.
Yatseniuk is a pro-Western former foreign minister and economy minister. One of his first major jobs would be preventing the Ukrainian economy from collapse.
The White House says it strongly supports Ukrainian leaders as they work to form a multiparty government to represent all Ukrainians. It calls a broad-based government committed to reconciliation the necessary foundation for international aid.
Secretary of State John Kerry says the U.S. is considering $1 billion in loan guarantees for Ukraine.
Russian Defense Minister Sergei Shoigu says the military exercises will check "readiness to deal with crisis situations that threaten the nation's military security."
The Kremlin did not superficially mention Ukraine. It has said it would not interfere in Ukraine's internal affairs. Ukraine is split between the pro-European west and the pro-Russian east and south.
Anti-government demonstrations erupted three months ago in Ukraine when Mr. Yanukovych backed out of a European Union trade deal in favor of economic aid from Russia. The violence escalated last week, leaving nearly 100 people dead.
Ukraine's interim leaders have dissolved an elite security force accused of carrying out some of those deadly attacks on protesters.