Since the emergency one-hour meeting was announced last Tuesday, Putin has signed laws completing Russia's annexation of the peninsula on the Black Sea and his troops seized a Ukrainian airbase there.

Leaders of the G-7 nations are to hold talks on the sidelines of a nuclear security summit in The Hague on Monday to consider their response to Russia annexing Crimea, amid doubts that sanctions can constrain President Vladimir Putin.

In what has become the biggest confrontation between the East and West since the Cold War, the United States and the European Union have imposed sanctions targeting some of his closest political and business allies, but it was unclear whether they went far enough to influence Moscow.

At The Hague, the G-7 will probably 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.

Western governments are struggling to find a balance between putting pressure on Putin, protecting their own economies and avoiding triggering a vicious cycle of sanctions and reprisals.

Dutch Prime Minister Mark Rutte, who is making his residence available to U.S. President Barack Obama and the leaders of Germany, Britain, Canada, France, Japan and Italy for the talks, said the West might want to move slowly.

"Russia has an economy that is highly focused on oil and gas," Rutte told Reuters. "It is not diversified ... If it came to putting in place sanctions, that would hurt Russia considerably. So in my view we should do everything to prevent that."



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U.S. officials say any further sanctions will need to be carefully calibrated to avoid bans on entire sectors, like oil or metals, that could reverberate through the global economy. Europe gets around one-third of its oil and gas from Russia.

British Foreign Secretary William Hague said in an article on Saturday, however, that Britain and its allies should consider imposing lasting limitations on arms sales to Russia, following the "outrageous" annexation of Crimea.

Diplomats said it was unlikely any detailed decisions about sanctions would be taken at the meeting, due to start at 6.30 p.m. (1730 GMT), although the group is likely to send a message of support for Kiev, particularly referring to Ukraine's battered economy.