Russian Foreign Minister Sergei Lavrov has told his US counterpart that Moscow "will respect the territorial integrity of Ukraine" but voiced concerns about the situation in southern Crimea.
US Secretary of State John Kerry said on Thursday that the pledge came in an early morning phone call with his Russian opposite number, who insisted Moscow was not behind the storming of Crimean government buildings by dozens of armed pro-Kremlin gunmen.
"I asked specifically that Russia work with the United States and our friends and allies in order to support Ukraine to rebuild unity, security and a healthy economy," Kerry told reporters.
Lavrov reaffirmed President Vladimir Putin's statement that Russia "will respect the territorial integrity of Ukraine", Kerry said after talks with German Foreign Minister Frank-Walter Steinmeier.
Lavrov also denied that Moscow had any hand in the takeover of the buildings in the Crimea, over which a Russian flag was hoisted on Thursday.
"On the contrary they are concerned about it, they expressed their concern about it," Kerry said.
But he warned that Washington would be keeping a close eye on events following the ousting of Russian-backed president Viktor Yanukovych to ensure that Russia stays true to its word.
"Statements are statements, words are words," Kerry said, adding "we have all learnt that it is action and the follow-on choices that make the ... difference."
The German minister meanwhile called on Moscow to work with the United States and the European Union (EU) to help Ukraine.
"No one will benefit from this country teetering on the brink of bankruptcy. We need political stabilisation to be accompanied by economic stabilisation," Steinmeier said.
He confirmed that the EU was thinking of offering about $US1 billion ($A1.12 billion) in loan guarantees to Ukraine, but said the International Monetary Fund first had to assess what was needed.
"It's difficult for anyone to give you an exact idea of how much Ukraine needs. Yanukovych has kept the figure hidden under his desk," Steinmeier said.
He insisted: "The political future is in the hands of the Ukrainians. It is for them to decide about their future and I hope they will do so in a way that will allow for an inclusive government that considers itself to be responsible for the people of the country as a whole."
Ukraine owes $US13 billion in state debt payments this year - a massive sum in a country where state reserves have shrunk to less than $US18 billion.
IMF chief Christine Lagarde said on Thursday that Kiev's new government of technocrats had made a formal request for IMF help and a fact-finding team was being dispatched to Kiev.
The White House meanwhile reinforced US warnings to Russia that it must avoid "miscalculations" in military drills along the border of Ukraine.
The comments appeared to reflect Washington's concern that Russian manoeuvres near the ex-Soviet state could trigger events that may get out of control.
Kerry said Lavrov had assured him that the exercises were long planned and had nothing to do with the fast-moving events in Ukraine.
But Carney cautioned: "We expect Russia to be transparent about these activities and to avoid provocative actions."
