Obama met Monday evening with his national security team, including secretary of state John Kerry and defense secretary Chuck Hagel, to discuss Ukraine.
Hours later, Kerry was to leave for Kiev to reinforce US support for the new Ukrainian government that only weeks ago ousted its pro-Russian president.
But French foreign minister Laurent Fabius said Russia's control of Crimea would not be easy to reverse.
And the suggestions he offered — sending in observers from the Organization for Security and Cooperation, questioning Russia's membership in the Group of Eight economic organization and holding out for a diplomatic dialogue proposed by Germany — were an indication of how limited the options were for the US and Europe.
Still, alternately threatening and cajoling Putin, Western leaders pointed to the damage that his nation's natural gas, uranium and coal industries could suffer if sanctions cut off exports to the European Union, its largest customer.
Britain's prime minister warned of diplomatic, political, economic "and other pressures" that could be brought against Moscow.
And the European Union's foreign ministers issued a Thursday deadline for Putin to pull back his troops or face a rejection of visa-liberalization and economic cooperation negotiations that have long been in the works.
