Roadside bombs remain a key concern for US and Iraqi forces
A roadside bomb targeting a Sunni tribal leader has exploded near the Iraqi city of Falluja, wounding him and killing three other people.
Naeem Saleh al-Halbusi is a local leader of the Awakening Council that has been supporting American troops.
The attack came as hundreds of thousands visited a major Baghdad shrine for a key Shia Muslim festival.
Such gatherings have in the past been frequent targets for attacks, but this one was relatively free of violence.
The BBC's Gabriel Gatehouse in Baghdad says the gathering represents the biggest test for the Iraqi security forces since US troops withdrew from the country's towns and cities at the end of June.
One of the dead in Saturday's bombing near Falluja, a former insurgent stronghold west of Baghdad, was the son of Mr Halbusi. Two bodyguards were also said to have died.
Mr Halbusi suffered shrapnel wounds.
The Awakening Council is a Sunni tribal movement that over the past few years has turned away from the insurgency to support the Americans.
The council is credited with helping to reduce insurgent activity dramatically.
Our correspondent says the Shia festival will have been a major test for the security forces.
Despite a partial curfew and tight security, a spate of bombings killed three pilgrims and wounded more than 30 others on Friday.
However, large scale attacks have so far been avoided.
Pilgrims visited the shrine of Imam Moussa al-Kadhim for one of the most important dates in the Shia religious calendar.
In 2005, at the same festival, rumours of a suicide bomber swept through the crowd causing a stampede that killed around 1,000 people.
Meanwhile, Iraqi police said they had arrested a member of an Iranian-backed militia suspected of involvement in the killing of three US soldiers in a rocket attack near Basra airport on Thursday.
Iraqi Maj Gen Adil Daham told Associated Press that Iranian-made rockets were seized from the suspect's house.