NEW : The cruise missiles strike more than 20 targets . UK : They were fired from U.S. and British ships and submarines . NATO : NATO expects the U.S. portion of the military operation to last just a few days , an official says .
NEW : Tomahawk cruise missiles strike more than 20 targets . NEW : They were fired from U.S. and British ships and submarines . NEW : Obama expects the U.S. portion of the military action to last just a few days , an official says .