Military officials said imposing an international no-fly zone looks unlikely, especially with support appearing to decline among Western allies.

On Monday, British Prime Minister David Cameron spoke enthusiastically about the idea, but on Tuesday senior British officials, facing skepticism from the U.S. and France, tempered their support.

U.S. military officials said if evidence grows that Col. Gadhafi is using airstrikes, especially against unarmed protesters, international support for a no-fly zone could shift.

For now, the most likely military intervention is a humanitarian relief effort in the eastern part of the country, the rebels’ stronghold. The Pentagon has sent two ships and a large contingent of U.S. Marines to the Mediterranean Sea. U.S. troops landing there would require air cover from American fighter planes, but face less of a threat from air defenses based in the western part of the country.