Six American soldiers were killed today in two separate roadside bomb attacks on patrols in Iraq, the U.S. military announced.

A Marine also was killed in western Iraq on Sunday by a roadside bomb, the military said today. The Marine was killed "while conducting combat operations against the enemy" in Amiriyah in western Anbar province, the military statement said.

Four of the soldiers killed today were slain in the town of Yusufiyah, just south of Baghdad, a statement from the military said. The two others were killed near Balad, 40 miles north of Baghdad, a second military statement said. The statements gave no other details.

The southern outskirts of the Iraqi capital, where the four servicemen died -- the heaviest single U.S. loss in some time -- is coined the "Triangle of Death" because of the considerable violence there by Sunni Arab insurgents against the country's ruling Shiites and the U.S. forces defending the Shiite-led Iraqi government. Balad, in the Tigris River Valley near Samarra, is a heartland of the Sunni insurgency.

U.S. and Iraqi forces mounted intensive searches around Baghdad Friday and Saturday, the military said. It said 49 suspected terrorists were arrested in the sweeps and a large amount of weapons and bomb-making materials were confiscated.