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Russia is unlikely to pull back its military forces in Ukraine's Crimean peninsula, analysts and former Obama administration officials say, forcing the United States and Europe into a more limited strategy of trying to prevent President Vladimir Putin from making advances elsewhere in the former Soviet republic.

It's an unsettling scenario for President Barack Obama, who is under pressure to show he has leverage over Putin in a deepening conflict between East and West. The threat of economic sanctions, along with a series of modest measures that include canceling trade talks with Moscow and suspending plans to attend an international summit in Russia, have so far done little to persuade the Russian leader to pull his forces back from Crimea.

"I'm not optimistic they're going to leave," said Michael McFaul, who served as Obama's ambassador to Russia until just last week.

McFaul, in an interview on MSNBC, said he was expressing his personal view, not speaking on behalf of the administration. White House officials have condemned Russia's military maneuvers in Crimea as a violation of international law and insist they would oppose any long-term occupation of the region.

"We would not find that to be acceptable," White House spokesman Jay Carney said Tuesday.

A senior administration official said it would be up to Ukraine's central government to decide the future of Crimea, where nearly 60 percent of the population identify themselves as Russians. The official said the U.S. would oppose any Russian efforts to formally annex Crimea or recognize its independence, steps that would echo Moscow's moves during its 2008 conflict with Georgia, another former Soviet republic.

Ukraine is in the midst of a monthslong political crisis sparked by ousted President Viktor Yanukovych's rejection of a partnership agreement with the European Union in favor of historical ties with Moscow. After Yanukovych fled Ukraine last week, Russian forces quickly moved into Crimea, despite Obama's warnings that there would be costs for violating Ukraine's territorial integrity.

Putin's fast and defiant dismissal of Obama's threats sparked a new round of criticism from the White House's Republican opponents. Sen. John McCain, R-Ariz., accused Obama of having "a feckless foreign policy in which nobody believes in America's strength anymore."

Obama and his advisers insist they still have an array of options at their disposal, the most stringent being economic sanctions that could go into effect as early as this week. The European Union appears to be treading more cautiously, but the bloc's 28 leaders are set to decide on initial sanctions at an emergency meeting in Brussels on Thursday.

But even with tough economic penalties, some regional analysts say it may already be too late to reverse course in Crimea.

"The idea that there's a contest over Crimea is a little silly," said Matthew Rojansky, a Russia analyst at the Wilson Center, a think tank in Washington. "It's in Russian hands and it was always on the verge of being in Russian hands."

Rojansky said the most pressing concern for the U.S. is instead to keep Putin from pushing into Russian-friendly areas of eastern Ukraine, where U.S. officials are warily eyeing ethnic skirmishes. Putin on Tuesday said he saw no reason for Russia to intervene there at the moment but added that he reserved the right to take that step if Russian speakers in the region were in danger.

The Crimean peninsula is separated from the rest of Ukraine by geography, history and politics. It only became part of Ukraine in 1954, when Soviet leader Nikita Khrushchev gave the peninsula to the republic where he began his political career, a transfer that hardly mattered until the Soviet Union broke up in 1991 and Crimea ended up in an independent Ukraine.

Crimea's port city of Sevastopol is also home to the Russian Black Sea Fleet and its thousands of naval personnel. Yanukovych, the ousted Ukrainian president, extended the fleet's lease until 2042, but Russia fears that Ukraine's temporary pro-Western government could evict it.

The U.S. is not calling for a full Russian withdrawal from Crimea, the Obama administration official said, but does want Moscow's forces to return to their normal operating position at their base, where they have an agreement with Ukraine to keep up to 11,000 troops. The official wasn't authorized to discuss the situation by name and would speak only on condition of anonymity.

The situation in Crimea has drawn comparisons to Abkhazia and South Ossetia, two breakaway territories of the former Soviet republic of Georgia. Russia has continued to maintain a military presence in both, violating a cease-fire that ended its 2008 military conflict with Georgia and ignoring repeated condemnations from the U.S. and Europe.

Barry Pavel, who worked on the White House National Security Council under both Obama and President George W. Bush, said reasserting control of Crimea may be even more important to Russia than the Georgian territories.

"Russian nationalists consider this to be practically Russian territory," said Pavel, who now serves as vice president of the Atlantic Council, a Washington-based think tank. "The chances of Russian forces ever leaving where they are are very low."

The long-term ramifications of Russia's remaining in Crimea are unclear, particularly as the rest of Ukraine works through its next steps following Yanukovych's ouster. But Heather Conley, a Europe analyst at the Center for Strategic and International Studies, said it would be a dangerous proposition for the U.S. and Europe to allow Putin to view gains in Crimea as an opportunity to launch incursions elsewhere in the region.

"Then this does start looking like appeasement," she said. "If you believe that more is in the offing, you have to take a stand now."

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