The military says one marine has been killed in the first day of a major U.S. Offensive against the Taliban in southern Afghanistan.Several other marines were wounded or injured during today's action.Marines poured into villages controlled by the Taliban along about 20 miles of the Helmand river.The marines said about 4,000 troops were involved in the offensive. The U.S. Military, meanwhile, says ``all available resources'' Are taking part in the search for an American soldier who disappeared Tuesday.