BRUSSELS, March 26 - The United States and the European Union agreed on Wednesday to work together to prepare possible tougher economic sanctions in response to Russia's behavior in Ukraine, including on the energy sector, and to make Europe less dependent on Russian gas.

U.S. President Barack Obama said after a summit with top EU officials that Russian President Vladimir Putin had miscalculated if he thought he could divide the West or count on its indifference over his annexation of Crimea.