WASHINGTON, March 25 (Reuters) - The United States has placed about 2,000 Marines with special operations training aboard Navy ships in the Gulf, poised for use in Afghanistan, where the hunt for al Qaeda and Taliban fugitives is intensifying, defense officials said on Thursday. U.S. commanders have not yet decided how many of the Marines deployed with the seven-vessel naval Expeditionary Strike Group, led by the amphibious assault ship USS Wasp, will be sent into Afghanistan, officials said. The Marines are from Camp Lejeune, North Carolina. The Wasp strike group, carrying 2,000 to 2,200 Marines from the 22nd Marine Expeditionary...