The East-West split reopened by the crisis in Ukraine hardened when US President Barack Obama threw Washington's weight behind Kiev in its stand-off with Moscow.
Obama welcomed Ukraine's interim premier, Arseniy Yatsenyuk, to the White House on Wednesday and appeared by his side as both leaders warned Russia that Ukraine would not surrender its sovereignty.
He repeated that Moscow would face unspecified "costs" if Russian President Vladimir Putin did not back down, and rejected a bid to hold what he called a "slapdash" referendum in Crimea.
"There's another path available and we hope President Putin is willing to seize that path," Obama said, sitting alongside Yatsenyuk after their talks at the Oval Office. "But if he does not, I'm very confident that the international community will stand firmly behind the Ukrainian government."
Yatsenyuk thanked Washington for its support and declared: "We fight for our freedom. We fight for our independence. We fight for our sovereignty. And we will never surrender."
After a series of meetings in Washington, Yatsenyuk was holding talks yesterday at the United Nations in New York.
Breakaway leaders on Ukraine's Crimean peninsula, backed by Putin, have called a referendum on Sunday on whether to split from Kiev.
Russian troops backed by ad hoc local militias secured the territory in the chaotic days last month after Ukraine's former pro-Kremlin leader, Viktor Yanukovych, was overthrown by a street revolt.
Obama said he hoped the crisis could be resolved through diplomacy. Ukraine and the West do not recognise the referendum. Moscow does not recognise the Kiev government.
The US leader appeared to suggest that Crimea's future was not set in stone, and that any change in status would be a matter for Ukraine's constitutional processes.
"There is a constitutional process in place and a set of elections that they can move forward on that, in fact, could lead to different arrangements over time with the Crimean region, but that is not something that can be done with the barrel of a gun pointed at you," Obama said.
"We have been very clear that we consider the Russian incursion into Crimea outside of its bases to be a violation of international law. And we have been very firm in saying that we will stand with Ukraine and the Ukrainian people in ensuring that territorial integrity and sovereignty is maintained."
Yatsenyuk said he was "ready and open" for talks with Russia. "We want to be very clear that Ukraine is and will be a part of the Western world," he said.
During his trip to Washington, Yatsenyuk hoped to iron out details of a US$35 billion aid package he says his nation's economy needs to stay afloat.
He met Christine Lagarde, managing director of the International Monetary Fund. He also visited the World Bank and briefed US lawmakers.
"If Russia goes further, this will totally and entirely undermine the global security," he said.