BAGHDAD – Gunmen in Iraq killed a Shiite cleric and an outspoken critic of sectarian militias in an ambush on a van carrying his wife, mother and sister, police said Sunday.

The cleric, Haider al-Saymari, was killed Saturday in the southern Iraqi city of Basra. His relatives were not harmed, said a police official who spoke on condition of anonymity because he was not authorized to release the information.

Al-Saymari, 38, was a follower of Iraq's top Shiite leader, Grand Ayatollah Ali al-Sistani, a moderate. Al-Saymari was known as a critic of extremists and armed groups in Basra, particularly the Mahdi Army militia of al-Sistani's rival, radical Shiite leader Muqtada al-Sadr.

Al-Saymari had lived and worked in the holy Iranian city of Qom since 1991, but returned to his native Iraq to take part in a Shiite religious ceremony earlier this month.

He was heading back to Iran Saturday, passing through downtown Basra, when gunmen firing from a car ambushed his van. Al-Saymari was rushed to a hospital where he was pronounced dead.

In other violence on Sunday, assailants attacked police patrols in Baghdad and Baqouba, northeast of the capital.

Gunmen driving an ambulance opened fire on a foot patrol in Baqouba, capital of the turbulent Diyala province, killing three policemen and wounding a bystander, police said.

In eastern Baghdad, assailants set off back-to-back roadside bombs.

The first bomb was detonated when a police patrol stopped in the area, according to Maj. Mark Cheadle, spokesman for U.S.-led coalition forces. When a quick response unit of the Iraqi security forces arrived at the scene, a second blast went off.

Cheadle said two Iraqis were killed and 13 people were wounded, including seven members of the security forces. Iraqi police reported three dead and 20 wounded.

Tens of thousands of Iraqi civilians have been killed in violence since the U.S.-led invasion of Iraq in 2003.

The number of roadside bombs, suicide attacks and sectarian killings has ebbed in recent months after a U.S. troop buildup, a Shiite militia cease-fire and a Sunni revolt against al-Qaeda in Iraq.