The U.S. military said in a statement the incident occurred in the volatile Anbar province, which includes the cities of Al-Fallujah and Ramadi.
The Marines did not release any other details about the attack, saying to do so could put other troops at risk.
More than 70 Marines died in an offensive to retake Al-Fallujah from rebels last month. Fighting is still going on in the city in some areas. Ramadi is effectively held by insurgents.
More than 1,000 U.S. troops have died in combat since the war in Iraq was launched.Marine Charged With Desertion
Meanwhile, a U.S. Marine who disappeared in Iraq only to later appear in Jordan claiming he had been kidnapped by insurgents has been charged with desertion.
U.S. Marine Corporal Wassef Ali Hassoun has been charged with taking unauthorized leave, loss of government property and theft of a military pistol.
The Marine Corps said the charges will now be considered by an investigating officer to determine if Hassoun will be court-martialed.
Hassoun -- who worked as an Arabic translator -- vanished from a U.S. military camp near Al-Fallujah in June.
The Lebanese-born marine appeared on Arabic television blindfolded and with a sword held above his head, but in July he walked into the U.S. Embassy in the Lebanese capital, Beirut.
(Reuters/AP/AFP) For more on events in Iraq, see RFE/RL's dedicated "The New Iraq" webpage.