The United States has warned Russia against any military intervention in Ukraine and revealed it is drawing up an economic aid package including $US1 billion ($A1.12 billion) in loan guarantees.
But US Secretary of State John Kerry also insisted on Wednesday that Washington was not looking for a confrontation with Moscow amid the political upheaval in the former Soviet satellite.
"A lot of people are looking at this and trying to define this in the context of the Cold War, the old fights. But I want to underscore to everybody that this is not Rocky 4. It is not a zero-sum game," Kerry said.
"We have only one interest and that is for the people of Ukraine to be able to make their choice, and to choose the path that they want to go down and for the rest of us to respect that path."
He insisted the top priority for the interim Ukraine leadership that has taken over after the exit of president Viktor Yanukovych was forming a new inclusive government, as he revealed that the United States was "formulating initially a $1 billion loan guarantee with some other pieces" in aid.
The European Union was also looking at offering $US1.5 billion ($A1.68 billion) in loan guarantees to the former Soviet satellite, he said.
The top US diplomat warned Russia that "any kind of military intervention that would violate the sovereignty, the territorial integrity, of Ukraine would be a grave mistake".
Although he was reluctant to say what the international response would be to any such military steps, he hinted there could be moves to take any such intervention to the United Nations.
Russian Defence Minister Sergei Shoigu said earlier on Wednesday that Moscow was taking measures to ensure the security of its Black Sea naval fleet based on Ukraine's southern Crimean peninsula.
Sevastopol, which has hosted the Black Sea fleet since tsarist times, has witnessed several pro-Russian demonstrations in recent days with hundreds rallying outside city hall on Tuesday.
"For a country that has spoken out so frequently in the last year ... and so strongly against foreign intervention in Libya and Syria and elsewhere, it would be important for them to heed those warnings as they think about options in the sovereign nation of Ukraine," Kerry told a reporters' roundtable in his private conference room.
