A suicide car bomber struck a U.S. patrol on Monday, killing four American soldiers and an interpreter in the northern city of Mosul, the military said.
It was the deadliest single attack against U.S. forces in more than nine months.
The explosion occurred near a police checkpoint in a volatile Sunni area in the northern city of Mosul, according to Iraqi police. The city has been dubbed the last urban stronghold of al-Qaida in Iraq by the U.S. military. It also has seen a rise in ethnic tensions amid a power struggle between Kurds and Arabs. The U.S. military said three soldiers were killed at the site when the bomber detonated his explosives-laden car near their vehicle, while another soldier and an interpreter died later of wounds from the explosion.
The deaths raised to at least 4,243 members of the U.S. military who have died in the Iraq war since it began in March 2003, according to an Associated Press count.
The number of Americans killed in action in Iraq has been declining along with an overall decline in violence nationwide. Only five of the 16 U.S. troop deaths last month were due to combat, the AP tally shows.
Four U.S. soldiers died when two helicopters crashed in the northern city of Kirkuk on January 26, but the military said that did not appear to be due to hostile fire.
The last time four U.S. troops were killed in a single attack was May 2, 2008, when four Marines died during combat in Anbar province, a former insurgent stronghold west of Baghdad.
An Iraqi police official, who spoke on condition of anonymity because he wasn't authorized to release the information, said three Iraqis, including two policemen, also were wounded in Monday's blast.