SIMFEROPOL, Ukraine - Masked gunmen stormed parliament in Ukraine's strategic Crimea region Thursday and raised the Russian flag as Russian fighter jets scrambled to patrol borders. The newly formed government in Kiev pledged to prevent a national breakup with strong backing from the West - the stirrings of a potentially dangerous confrontation reminiscent of Cold War brinksmanship.
A group of armed men in military uniform but no signs of identification seized Simferopol Airport in Crimea in the early hours of Friday, according to a report from the Interfax news agency.
The report could not be immediately confirmed, but it underscored the heightened tensions in the region.
As gunmen wearing unmarked camouflage uniforms erected a sign reading "Crimea is Russia" in the provincial capital, Ukraine's interim prime minister declared the Black Sea territory "has been and will be a part of Ukraine."
The escalating conflict sent Ukraine's finances plummeting further, prompting Western leaders to prepare an emergency financial package.
Yanukovych, whose abandonment of closer ties to Europe in favor of a bailout loan from Russia set off three months of protests, finally fled by helicopter last week as his allies deserted him. The humiliating exit was a severe blow to Russian President Vladimir Putin, who had been celebrating his signature Olympics even as Ukraine's drama came to a head. The Russian leader has long dreamed of pulling Ukraine - a country of 46 million people considered the cradle of Russian civilization - closer into Moscow's orbit.
In the Crimean capital, Simferopol, demonstrators chanted, "Russia, Russia!" Some 60 percent of Crimea's residents are ethnically Russian, and many of them see the new Ukrainian leadership as illegitimate.
"We cannot accept the authority in Kiev. We are a different people," demonstrator Ludmila Milodanova said. "We will be happy to join Russia. It is our motherland."
For Ukraine's neighbors, the specter of Ukraine breaking up evoked memories of centuries of bloody conflict.
"Regional conflicts begin this way," said Polish Foreign Minister Radoslaw Sikorski, calling the confrontation "a very dangerous game."
In Kiev, a 20-year-old student named Tanya told CBS News' Clarissa Ward she is nervous about what Russia might do.
"They are a powerful country," Tanya said. "They can do bad things with us."
Russia has pledged to respect Ukraine's territorial integrity. But the dispatch of Russian fighter jets Thursday to patrol borders and drills by some 150,000 Russian troops - almost the entirety of its force in the western part of the country - signaled strong determination not to lose Ukraine to the West.
In Washington, U.S. Secretary of State John Kerry said Moscow has told the United States that military exercises near the Russian-Ukraine border are not a prelude to any intervention.
Kerry had earlier warned Russia against any military intervention in the former Soviet republic and said any such action could face a strong response from the West, though he did not specify what that might be.
"We will look to Russia for the choices that it makes in the next days for their confirmation of these statements," Kerry said Thursday at a State Department news conference with German Foreign Minister Frank-Walter Steinmeier. "Words are words. We have all learned that it's actions and the follow-on choices that make the greatest difference."
Kerry predicted that the military exercise will not be "so prolonged that it is going to have an impact on events there."
"Everybody needs to step back and avoid provocations," Kerry said.In Brussels, U.S. Defense Secretary Chuck Hagel urged Russia not to take any action on Ukraine that could be misinterpreted.
At a news conference after a NATO defense ministers' meeting, Hagel said the U.S. is closely watching Russia's military exercises and that Washington strongly supports Ukraine's territorial integrity. He said the U.S. expects all nations to respect Ukraine's sovereignty and avoid provocations.
"This is a time for very cool, wise leadership, on the Russian side, and on everybody's side," Hagel said.Thursday's dramatic developments posed an immediate challenge to Ukraine's new authorities as they named an interim government for the country, whose population is divided in loyalties between Russia and the West. Crimea, which was seized by Russian forces in the 18th century under Catherine the Great, was once the crown jewel in Russian and then Soviet empires.
It only became part of Ukraine in 1954 when Soviet leader Nikita Khrushchev transferred jurisdiction from Russia - a move that was a mere formality until the 1991 Soviet collapse meant Crimea landed in an independent Ukraine.
In the capital, Kiev, the new prime minister said Ukraine's future lies in the European Union, but with friendly relations with Russia.
Arseniy Yatsenyuk, named Thursday in a boisterous parliamentary session, now faces the difficult task of restoring stability in a country that is not only deeply divided politically but on the verge of financial collapse. The 39-year-old served as economy minister, foreign minister and parliamentary speaker before Yanukovych took office in 2010, and is widely viewed as a technocratic reformer who enjoys the support of the U.S.
Shortly before the lawmakers chose him, Yatsenyuk insisted the country wouldn't accept the secession of Crimea. The Black Sea territory, he declared, "has been and will be a part of Ukraine."
In Simferopol, the Crimean regional capital, gunmen toting rocket-propelled grenades and sniper rifles raised the Russian flag over the local parliament building. They wore black and orange ribbons, a Russian symbol of victory in World War II.
Oleksandr Turchynov, who stepped in as acting president after Yanukovych's flight, condemned the assault as a "crime against the government of Ukraine." He warned that any move by Russian troops off of their base in Crimea "will be considered a military aggression."
"I have given orders to the military to use all methods necessary to protect the citizens, punish the criminals, and to free the buildings," he said.
Experts described a delicate situation in which one sudden move could lead to wider conflict.
"The main concern at this point is that Kiev might decide to intervene by sending law enforcement people to restore constitutional order," said Dmitry Trenin, head of the Carnegie Moscow Center. "That is something that would lead to confrontation and drag the Russians in."
In a bid to shore up Ukraine's fledgling administration, the International Monetary Fund said it was "ready to respond" to Ukraine's bid for financial assistance. The European Union is also considering emergency loans for a country that is the chief conduit of Russian natural gas to western Europe.
IMF chief Christine Lagarde said in the organization's first official statement on Ukraine's crisis that it was in talks with its partners on "how best to help Ukraine at this critical moment in its history." Ukraine's finance ministry has said it needs $35 billion over the next two years to avoid default. Ukraine's currency, the hryvnia, dropped to a new record low of 11.25 to the U.S. dollar, a sign of the country's financial distress.
Western leaders lined up to support the new Ukrainian leadership, with the German and British leaders warning Russia not to interfere.
"Every country should respect the territorial integrity and sovereignty of the Ukraine," British Prime Minister David Cameron said after a meeting with German Chancellor Angela Merkel in London.