President Barack Obama demanded Friday that Libyan leader Moammar Gadhafi immediately halt all attacks against civilians and withdraw his forces from several cities, vowing military action if he fails to comply with a United Nations resolution that authorized the use of "all necessary measures" to protect civilians in Libya.

The demands came as reports of fighting on the coastal highway 30 miles from the rebel capital of Benghazi and bombardments of the city of Misrata in the west ran counter to Libyan Foreign Minister Moussa...