BAGHDAD — Iraqi authorities have arrested a member of an Iranian-backed militia suspected in an attack that killed three U.S. soldiers in southern Iraq, police said yesterday.

Meanwhile, to the west of Baghdad, bombs killed five people, including the son of a tribal leader.

Maj. Gen. Adil Daham, chief of the Basra provincial police, said the militiaman confessed early yesterday to the attack on a U.S. base near the airport. The soldiers were killed Thursday night in a rocket attack, the U.S. military said, in a rare assault on troops in the comparatively quiet south.

As of yesterday at least 4,327 members of the U.S. military had died in the Iraq War since it began in March 2003, according to an Associated Press count.

During a search of the house where the suspect and an aide were arrested, Iraqi officials say they seized four Iranian-made rockets and documents listing names of officials to be targeted.

U.S. military commanders believe some Shiite militias have received funds and training from Iran, which denies the charge.

Yesterday, a bomb struck the vehicle of Sunni leader Sheik Naeim Salih al-Halbosi as he was leaving his house near Fallujah, police said.

Al-Halbosi was wounded, but his son and two guards were killed, an officer said on condition of anonymity because he wasn't authorized to talk to the media.

Al-Halbosi is a member of a tribal council cooperating with the Shiite-led government on security in the Fallujah region that has helped dramatically reduce insurgent activity in the area.