Four U.S. troops died in fighting in western Iraq on Monday, the U.S. military said on Tuesday, taking to at least 1,935 the number of U.S. forces killed since the invasion of Iraq in March 2003. One Marine was killed by an improvised bomb in Karabila, near the Syrian border, during a major military operation called Iron Fist, a statement said. Three soldiers were killed by improvised bombs in Haqlaniya, in the western Anbar province, the U.S. military was quoted as saying by Reuters.