A suicide bomber detonated an explosive vest at a dinner feast in western Baghdad's Abu Ghraib district on Sunday, killing 25 people, police said.
The attack, the biggest in weeks, took place at the home of a local sheikh who was holding the feast to celebrate the release of his son from U.S. detention, police said.
They said women and children were among the dead, as were some men believed to be members of U.S.-backed neighborhood patrols.
Police colonel Dawood Suleiman in the nearby city of Fallujah gave the initial death toll as 21. A police source in Baghdad who declined to give his name later said 25 had died and 32 were injured.
Abu Ghraib is a largely Sunni Arab district located between central Baghdad and Fallujah on the main highway heading west from the capital.
U.S. and Iraqi authorities say suicide bombings are the signature tactic of al Qaeda Sunni Arab militants, who frequently target other Sunnis since Sunni tribes turned against them over the past two years.
Iraq has become far less dangerous over the past year, but militants still retain the capability to conduct large-scaled bombings.
Also Sunday, the U.S. military announced Sunday the arrest of an al-Qaida figure who allegedly planned the 2006 kidnapping of American journalist Jill Carroll.
A statement said Salim Abdullah Ashur al-Shujayri was captured during an Aug. 11 operation. It says he is also known as Abu Othman.
The military says al-Shujayri is believed to be "the planner behind the kidnapping" of Carroll. She was a Christian Science Monitor reporter seized Jan. 7, 2006, and freed three months later.
The statement also says al-Shujayri's associates were involved in the high-profile kidnappings of Christian peacemakers and British aid worker Margaret Hassan.
Hassan was abducted in Baghdad in October 2004 and later killed, although her body was never found. 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.
Shiite cleric wounded
In other Iraq news, the cleric, Haider al-Saymari, was wounded 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. An earlier report said he had died.
Al-Saymari, 38, is a follower of Iraq's top Shiite leader, Grand Ayatollah Ali al-Sistani, a moderate. Al-Saymari is 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 being treated for serious injuries.
Assailants attack police patrols
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-Qaida in Iraq.