BAGHDAD, Iraq - A man dressed as a policeman blew himself up Saturday at the heavily guarded Baghdad headquarters of a feared commando unit, killing at least three people, officials said. Witnesses said at least five died, not including the bomber.

Three other commandos were killed in an attack on their convoy in western Baghdad's Mansour area, police said.

Separately, at least 11 Iraqi construction workers were killed and three wounded when gunmen opened fire on their minibus in Diyara, 30 miles south of Baghdad. The men worked on projects on Iraqi and American bases, police said.

Two U.S. Marines were killed Friday in a roadside bomb attack near the volatile Anbar province town of Saqlawiyah, west of Fallujah, the military said Saturday. At least 1,693 U.S. military members have died since the Iraq war began in March 2003, according to an Associated Press count.

The suicide bombing targeted the headquarters of the Wolf Brigade, a commando force dominated by Shiite Muslims. Sunni Arab leaders have accused the force of kidnapping and killing members of Iraq's minority Sunni community, including clerics.

Interior Minister Bayan Jabr said the attacker was a former Wolf Brigade member who was targeting the force's commander, Brig. Mohammed al-Quraishi.

"Today's attack does not constitute an infiltration of the police forces," Jabr said during a news conference. "The only thing left of the bomber was his head and feet."

Police are hunting two of his former colleagues, the minister added.

Jabr said three people were killed. But a witness to the attack, Maj. Falah al-Mahamdawi, said five people were killed and seven wounded.

It was unclear how the attacker managed to elude detection at the compound in eastern Baghdad's Bab Sharqi neighborhood. The police uniform he was wearing may have enabled him to avoid stringent checks for explosives.

People who want to enter the compound, which also houses the Interior Ministry, must first go through metal detectors, be frisked by policemen and checked by sniffer dogs.

Al-Mahamdawi, the police officer, said the attacker was disguised as a policeman and detonated explosives during a roll call for recently graduates. It was unclear if the bomber was standing among the graduates or was nearby.

The attack may have been motivated by the Sunni struggle for a role in the country's political process. Sunnis, a minority favored by Saddam Hussein, resent the rise to power of the majority Shiite community and the U.S.-allied Kurds.

This is believed to be a major factor in the continuing insurgency in Iraq that has killed more than 900 people since the new Shiite-led government was announced April 28.

In another attack in Baghdad, 10 people were killed late Friday when a car bomb exploded outside a restaurant in Baghdad, Dr. Ali Khazim of Nour Hospital said Saturday. Two children were among the dead, while another 28 were wounded.

Iraqi police also raided an auto mechanic's workshop in the southeastern New Baghdad suburb and captured five men suspected of rigging car bombs, Lt. Col. Ahmed Abood said. It was unclear in which attacks the men were allegedly involved.