Ukraine says it won't intervene in Crimea

Ukraine's acting president has said the country will not use its army to stop Crimea from seceding, the latest sign that a Russian annexation of the strategic peninsula may be imminent.

Oleksandr Turchynov's Tuesday comments came after the Crimean parliament voted for independence ahead of a referendum on joining Russia, while Washington and Moscow locked horns in one of their fiercest clashes since the Cold War.

The interim leader said intervening on the southeastern Black Sea peninsula, where Kremlin-backed forces have seized de facto control, would leave Ukraine exposed on its eastern border, where he said Russia has massed "significant tank units".

"We cannot launch a military operation in Crimea, as we would expose the eastern border and Ukraine would not be protected," Turchynov told 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."

Sunday's referendum is being organised by Crimea's self-appointed leaders, who are not recognised by the new pro-European government in Kiev, installed after three months of protests that resulted in 100 deaths and the ouster of pro-Russian president Viktor Yanukovych.

Conversely, Turchynov is not recognised by Moscow, which still insists Yanukovych is Ukraine's legitimate president.

Turchynov described the secession referendum as a "sham" whose outcome would be decided "in the offices of the Kremlin".

World powers have repeatedly called for Moscow and Kiev to come together to seek a solution to the escalating crisis, but Turchynov said Russia's leaders were refusing any such talks.

"Unfortunately, for now Russia is rejecting a diplomatic solution to the conflict," he said.

Western powers, led by the US and Germany, insist that forming an "international contact group" is the way out of the crisis over the culturally fractured ex-Soviet state, which erupted into protest after Yanukovych pulled out of a deal on closer ties with the European Union in favour of a now-frozen bailout from Russia.

Turchynov's comments came as Ukrainian Prime Minister Arseniy Yatsenyuk headed to the White House for a meeting on Wednesday with US President Barack Obama that should add credibility to his untested team.

Yatsenyuk will also use the visit to iron out the details of a $US35 billion ($A39.10 billion) aid package he says his country's teetering economy needs to stay afloat over the next two years.

The European Union has also announced trade breaks worth 500 million euros ($A777.97 million) that could ease Ukraine's burden from restrictions that Russia has threatened in response to Kiev's tilt toward the West.

The White House is leaving no doubt about the message it intends to send Russia with the visit.

Yatsenyuk will be treated like any other foreign leader visiting Washington, and be greeted by Obama in the Oval Office - a symbol of US power - for talks and a short photo opportunity at which both men will make remarks.