BAGHDAD — The U.S. military said today a roadside bomb killed four Marines in western Anbar province — the deadliest attack in that area in months.

The Marines were killed Friday, but no other details of the incident were released.

Anbar was once a stronghold for insurgents battling against U.S. forces. But in the past year the vast desert province has largely been calmed with the rise of the Awakening Council movement — Sunni fighters who now turn their guns on al-Qaida instead of U.S. forces.

Thursday's attack was the most lethal in Anbar since Sept. 6, when four Marines were killed in combat. The military did not release details of those deaths.

On April 22, two Marines were killed in Anbar when a bomb-rigged truck exploded at a checkpoint in the city of Ramadi.

Commanders say the security situation in the province has greatly improved since fierce fighting in the city of Fallujah in 2004 came to symbolize Sunni resistance to the U.S. presence in Iraq.

Meanwhile, Iraqi health officials said at least 10 people — including two children — were killed in the past 24 hours in the Baghdad neighborhood of Sadr City, a slum of 2.5 million people and a stronghold for the Shiite Mahdi Army militia.

Officials at two hospitals in Sadr City spoke on condition of anonymity for security reasons.

U.S. and Iraqi forces have been battling militia members there for weeks as part of an Iraqi government crackdown on the fighters.

On Saturday, the U.S. military fired guided missiles into the heart of Sadr City, leveling a building 50 yards away from a hospital and wounding nearly two dozen people.

AP Television News footage showed several ambulances destroyed and on fire, with thick black smoke rising from them as firefighters worked to put out the flames.

The strike, made from a ground launcher, took out a militant "command-control center," the U.S. military said. Iraqi officials said at least 23 people were wounded, though none of them were patients in the hospital.

The clashes with the Mahdi Army have brought deep rifts among Iraq's Shiite majority and have pulled U.S. troops into difficult urban combat.

Militia members have been blamed for firing hundreds of rockets or mortars from Sadr City into the Green Zone, the U.S.-protected area housing the American embassy and much of the Iraqi government.

In the past month, more than a dozen people — including two American civilians and soldiers — have been killed inside the zone during the attacks.