THE HAGUE/FEODOSIA, Ukraine - US President Barack Obama began crisis talks with his European allies on Monday after Ukraine announced the evacuation of its troops from Crimea, effectively yielding the region to Russian forces which stormed one of Kiev's last bases there.
Obama, who has imposed tougher sanctions on Moscow than European leaders over its seizure of the Black Sea peninsula, will seek support for his firm line at a meeting with other leaders of the G7 - a group of industrialised nations that excludes Russia, which joined in 1998 to form the G8.
Since the emergency one-hour G7 meeting was announced last week, Putin has signed laws completing Russia's annexation of the region.
In what has become the biggest East-West confrontation since the Cold War, the United States and the European Union have imposed visa bans and asset freezes on some of Putin's closest political and business allies. But they have held back so far from measures designed to hit Russia's wider economy.
"Europe and America are united in our support of the Ukrainian government and the Ukrainian people," Obama said after a meeting with Dutch Prime Minister Mark Rutte. "We're united in imposing a cost on Russia for its actions so far. Prime Minister Rutte rightly pointed out yesterday the growing sanctions would bring significant consequences to the Russian economy."
Moscow formally annexed Crimea on March 21, five days after newly-installed pro-Moscow regional leaders held a referendum that yielded an overwhelming vote to join Russia. Kiev and the West have denounced the annexation as illegal.
Western officials are now focussed less on persuading Putin to relinquish Crimea - a goal that seems beyond reach - than on deterring him from seizing other parts of Ukraine.
"Our interest is not in seeing the situation escalate and devolve into hot conflict," White House national security adviser Susan Rice told reporters. "Our interest is in a diplomatic resolution, de-escalation, and obviously economic support for Ukraine, and to the extent that it continues to be necessary, further costs imposed on Russia for its actions."
In The Hague, leaders of the G7 - the United States, Japan, Canada, Germany, France, Britain and Italy - will discuss how to exert further pressure - and at what potential cost.
"It will be an opportunity for us to explain to each other what we are doing and where we are going, to coordinate our actions," a senior EU official said.
Persuading Europeans to sign on to tougher sanctions could be a challenge for Obama. The European Union does 10 times as much trade with Russia as the United States, and is the biggest customer for Russia oil and gas. The EU's 28 members include countries with widely varying relationships to Moscow.
"Europeans are committed to do something," said Jeffrey Mankoff, an analyst at the Center for Strategic International Studies. "I think it'll be difficult to convince them to go anywhere near where the United States would like to go."