Ukraine's prime minister heads for talks Wednesday with US President Barack Obama aimed at winning vital aid and moral backing amid Crimea's plans to join Russia in the worst East-West crisis since the Cold War.
The first meeting between Obama and Prime Minister Arseniy Yatsenyuk comes with the vast ex-Soviet nation in danger of breaking apart when the predominantly ethnic Russian region holds a Moscow-backed referendum Sunday on switching over to Kremlin rule.
Ukraine's acting President Oleksandr Turchynov said his heavily outnumbered army would never try to seize back the Black Sea peninsula from Russian troops who made their land grab days after the February 22 ouster in Kiev of pro-Kremlin leader Viktor Yanukovych.
"We cannot launch a military operation in Crimea, as we would expose the eastern border and Ukraine would not be protected," Turchynov said in an interview with AFP.
Russia's first invasion of a neighbour since its brief 2008 war with Georgia has sparked both an explosive European security crisis and the worst breakdown in the Kremlin's relations with the West since the 1989 fall of the Berlin Wall.
The United States has imposed travel bans and asset freezes on Russians held responsible for violating the territorial integrity of the culturally splintered nation of 46 million.
The European Union -- its financial and energy sectors much more dependent on Russia than those of the United States -- has threatened to follow suit imminently after suspending free travel and economic talks with Moscow last week.
The standoff has also seen US Secretary of State John Kerry deliver a snub of immense diplomatic proportion by refusing a visit to Moscow that could have included a meeting with Russian President Vladimir Putin.
But this show of Western outrage at the actions of Putin -- who once called the breakup of the Soviet Union the biggest geopolitical tragedy of the 20th century -- has not kept him from taking Crimea under his control and threatening to use force to "protect" the interests of ethnic Russians living in the east of Ukraine.
The international community's almost unanimous rejection of the referendum's legitimacy has done little to slow the pace of Russia's attempt to redraw Europe's post-war borders and retake a region that was only handed to Ukraine as a symbolic "gift" when it was still a part of the Soviet empire in 1954.
Russia's parliament is due on March 21 to consider legislation that would simplify the procedure under which Moscow can annex a part of another country that has proclaimed independence -- as Crimea did Tuesday.
Ukraine's soldiers and marines have won plaudits from Western leaders for refusing to open fire against Russian troops and Kremlin-backed militia who have encircled their bases and kept their ships from going out to sea.
Acting president Turchynov said he as commander in chief realised fully the futility of launching an all-out war against a much larger invading force that had backing from nuclear weapons and tens of thousands of additional troops positioned just inside Russia.
"Significant tank units are massed near Ukraine's eastern border," Turchynov said in the interview with AFP.
"They're provoking us to have a pretext to intervene on the Ukrainian mainland... (but) we cannot follow the scenario written by the Kremlin."
Putin has accused Turchynov and Yatsenyuk of rising to power through an "unconstitutional coup" that came at the apex of three months of pro-Western protests that claimed 100 lives and forced Yanukovych to flee to Russia.
Turchynov said Moscow has refused all of his overtures for dialogue despite efforts by leaders such as German Chancellor Angela Merkel to set up in "international contact group" through which all sides could air their grievances in search of a compromise.
"Unfortunately, for now Russia is rejecting a diplomatic solution to the conflict," said Turchynov.
"They are refusing all contact at foreign ministry and top government level."
The acting president also rubbished as "madness" claims that Russian-speakers in Ukraine faced discrimination following the rise new and more nationalist leaders to power in Kiev.
The White House is leaving no doubt about the message it intends to send to Russia with the visit of Yatsenyuk -- a leader Moscow considers illegitimate.
He will be greeted like any other foreign leader by Obama in the Oval Office -- a symbol of US power -- and also meet Joe Biden after the US Vice President rushed back from a trip to South America to take part in the talks.
Washington says the reception for Yatsenyuk is intended to show it believes that the interim government in Kiev has been playing a responsible role in the crisis.
"We strongly support Ukraine, the Ukrainian people and the legitimacy of the new Ukrainian government," White House spokesman Jay Carney told reporters.
But Carney also stressed that the White House was still offering the Kremlin an "off ramp" for ending the dispute without any bloodshed and with Ukraine's territorial integrity held intact.
Yatsenyuk will also use the chance to iron out the details of a $35 billion aid package he says his nation's teetering economy needs to stay afloat over the coming two years after being mismanaged by president Viktor Yanukovych -- now living in self-imposed exile in Russia.
The White House said Obama would discuss an economic support package that has already seen Washington pledge more than $1 billion and the European Union 11 billion euros over two years.