LONDON (AP) -- The West braced Friday for a vote by the Crimean Peninsula to secede from Ukraine -- and likely be annexed by Russia -- as the last attempt for diplomacy broke down despite threats of costly international sanctions and other imminent penalties against Moscow for forcibly challenging a pro-European government in Kiev.
Russia's top diplomat said Moscow will make no decisions about Crimea's future, including whether to embrace it as a new territory, until after a local referendum Sunday to decide whether it should remain part of Ukraine.
But U.S. Secretary of State John Kerry said the vote's results are all but a foregone conclusion, and urged Russia's parliament against accepting any offer to claim Crimea as its own.
"We believe that a decision to move forward by Russia to ratify that vote officially within the Duma would, in fact, be a backdoor annexation of Crimea," Kerry told reporters in London after six hours of talks Friday with Russian Foreign Minister Sergey Lavrov.
Kerry instead called on Moscow to support broad autonomy for Crimea -- still as part of Ukraine -- instead of a move by the strategic peninsula to secede. And he predicted the probability of "if the people of Crimea vote overwhelmingly, as one suspects they will, to affiliate or be associated with Russia."
Crimea, which is Ukraine's strategic Black Sea peninsula of 2 million people, has a majority ethnic Russian population and hosts a large Russian naval base. The West and Ukraine's upstart government in Kiev believes the region's vote to secede is unconstitutional. But Moscow doesn't recognize leaders in Kiev as legitimate since they pushed Ukraine's pro-Russian president from power last month.
Lavrov, speaking separately to reporters, said Russia would respect the results of the Crimea vote but would not predict what would happen next.
"We lack a common vision of the situation, and differences remain," Lavrov said of his Ukraine negotiations with Kerry before heading back to Russia.
However, he said Moscow has no plans to invade southeast regions in Ukraine. Thousands of Russian troops amassed on Ukraine's eastern border this week, including large artillery exercises involving 8,500 soldiers in the Rostov region alone.
U.S. officials have derided the exercises as an intimidation tactic and noted that Russian President Vladimir Putin ordered a similar buildup of troops in and around Crimea immediately before pro-Russian forces in the region overtook the local government and began policing streets with militias.
The diplomatic stalemate marked a disappointing and last-ditch effort by the West to avoid a new diplomatic chill from growing between Putin and Europe and the U.S. The showdown has been cast as a struggle for the future of Ukraine, a country with a size and population similar to France.
Much of western Ukraine favors ties with the 28-nation European Union, while many in the eastern part of the country have closer economic and traditional ties to Russia. Putin has worked for months to press Ukraine back into Russia's political and economic orbit.
The West has resisted threatening the use of military force to keep Putin in check. Instead, officials have warned Moscow it will face a series of harsh sanctions against Russian officials and businesses, as well as others in Ukraine, who undermined the new government in Kiev that took over after deadly protests demanding economic opportunities offered in the West.
The EU and U.S. will impose sanctions as early as Monday.
"If the referendum takes place, there will be some sanctions," Kerry said. "There'll be some response."
British Prime Minister David Cameron echoed the sanctions threat.
"We want to see Ukrainians and the Russians talking to each other," Cameron told Kerry in a separate meeting Friday in London. "And if they don't, then there are going to have to be consequences."
But Lavrov issued his own warning that sanctions could further entrench Russia.
"Our partners also realize that sanctions are counterproductive," he said.
U.S. Sen. John McCain, in Kiev on Friday, pledged to help send an array of armaments, ranging from combat infantry rifles to anti-tank weapons, to Ukraine as quickly as possible. Ukraine's military is largely poorly trained, but McCain pointed to the looming Russian troops as enough reason to help the country defend itself.
"Would you like them to throw rocks?" said McCain, a hawkish Republican from Arizona. "If that's what they're literally begging for, why should we judge whether we give it to them or not?"
Ukraine's best hope now is for Crimea to declare autonomy but remain a part of the country.