BAGHDAD — A suicide car bomber yesterday attacked a police headquarters in Basra, killing at least three policemen, wounding 20 people and raising fears about security in the oil-rich southern city now that British forces have withdrawn.

It was the second major suicide attack to kill Iraqi police in as many days. The police chief of Baqouba was among at least 24 people killed when a suicide bomber attacked a Sunni-Shiite reconciliation meeting late Monday. An Al Qaeda front group yesterday claimed responsibility for the attack in Baqouba, 35 miles northeast of Baghdad.

Basra’s police chief, Major General Abdul-Jalil Khalaf, said the suicide bomber’s legs were found tied to the steering wheel — clearly an attempt by the attack’s planners to prevent the driver from running away.

Mr. Khalaf blamed Al Qaeda in Iraq for the attack, even though the terror movement was believed to have virtually no presence in the Basra area.

The attack occurred about 8 a.m. when the driver, wearing a traditional Arab robe and headgear, tried to steer his explosives-laden sedan into the downtown police headquarters building but was blocked by concrete barriers, Mr. Khalaf said.

The blast damaged nearby buildings and set several parked cars ablaze, witnesses reported.

Fears about security in Basra have been mounting since the British army left its last position within the city on September 2 and redeployed to the municipal airport, about 20 kilometers (12 miles) to the north.

For more than two years, Basra, Iraq’s second-largest city and headquarters of the country’s vast southern oil fields, has been racked by violence from rival Shiite militias that have infiltrated police and government ranks.

Several of the biggest militias are associated with major Shiite political parties.

But suicide attacks — the hallmark of Sunni religious extremists — are rare in the mostly Shiite city. Officials were quick to point the finger at Al Qaeda in Iraq, a Sunni extremist group.

“It seems that Al Qaeda wants to make use of the fragile situation in the city caused by the tension among the parties and the city’s officials,” Mr. Khalaf said.

He said authorities had been devoting most of their resources to nighttime patrols but would increase the number of police and soldiers on the streets during the daytime.

In Baghdad, at least 15 people were killed or found dead yesterday — apparent victims of political or sectarian violence, according to police reports. In the deadliest attack, a pair of car bombs exploded almost simultaneously near a line of elderly people waiting to get their monthly pensions from a bank, killing six people.

Gunmen killed police Lieutenant Colonel Ali Sameen, director of emergency services in Tuz Khormato, 130 miles north of Baghdad, police reported. The officer was gunned down yesterday near his home, police reported.

North of the capital in Diyala province, a roadside bombing killed an American soldier yesterday, the American command said.