WASHINGTON (Reuters) - One report reaching the U.S. military said that some of the 12 soldiers whose supply convoy was ambushed near Nassiriya in southern Iraq on Sunday were killed by their captors although they tried to surrender, a U.S. defense official said on Wednesday. The official, speaking on condition of anonymity, said the report received from the field said that the U.S. soldiers "weren't given the opportunity to surrender. They attempted to surrender." Some of the U.S. soldiers instead were killed by the Iraqi forces, the official said. The official did not characterize the nature or reliability of...