A US soldier was killed by an explosion during fighting northwest of Baghdad, while a Marine died in a non-combat incident, the military said Friday. The Task Force Lightning soldier died and another was wounded Thursday in an attack while they were conducting combat operations in Salahuddin, a mainly Sunni province, according to a statement. A Marine assigned to Multinational Force - West died Wednesday in a non-combat related incident in Anbar province, a Sunni insurgent stronghold west of the capital, the military said separately. The incident is currently under investigation. Identities were not released pending notification of relatives.