The bombing occurred a few hours before a funeral march was held in the Iraqi capital to mourn two traffic policemen who were killed in a battle with gunmen on Tuesday.
Wednesday's attack in the western city of Ramadi was carried out by a suicide bomber driving a minibus who struck a checkpoint of Iraqi soldiers and police, killing a policeman and five civilians, said a local police officer. Earlier reports said six policemen were among the dead.
The attack injured an additional 19 people, including five police, said the officer in Ramadi, which is located some 70 miles (115 kilometers) west of Baghdad. The officer spoke on condition of anonymity because he was not authorized to talk to the media.
Anbar used to be a stronghold of the Sunni insurgency but has been relatively quiet in recent months, partly because Sunni tribal leaders joined up with U.S.-led forces to fight extremists.
In Baghdad, dozens of mourners, including senior officials from the Interior Ministry, attended the funeral of the two traffic policemen who were killed in eastern Baghdad. Fellow traffic police motorcyclists led the funeral procession, which included the slain officers' wooden caskets wrapped in Iraqi flags.
The officers, Jassim Shuwaili, 24, and Hussein Qassim, 19, were chasing two gunmen in a speeding car after they refused to stop at a checkpoint near Baghdad's fortified Green Zone, according to Maj. Gen. Zuhair Ebada, head of traffic police operations in Baghdad's east side. One of the gunmen, who was later arrested, opened fire and killed the two motorcycle policemen.
Qassim, who joined traffic police six months ago, is survived by a wife and nearly two-year old baby. Shuwaili, who had three years of service on the force, was single.
"We ask the government to implement the ultimate the penalty against the criminals ... The martyr was serving his country and people," said Shuwaili's brother-in-law, Rafid Abdul-Hussein.
Separately, one person was killed and nine others were wounded when a bomb exploded near an Internet cafe late Tuesday night in south Baghdad. The explosion in a Shiite enclave in the mainly Sunni neighborhood of Dora damaged the cafe and a nearby shop.