BAGHDAD — A suicide car bomber targeted the provincial police headquarters in Mosul yesterday, killing at least nine people and wounding dozens, police said. The attack underscored fears that Sunni insurgents are regrouping despite an American-Iraqi offensive in the northern city.

Nobody claimed responsibility for the attack, but suicide operations are commonly associated with Al Qaeda in Iraq — the main target of American-Iraqi military operations to clear the city 225 miles northwest of Baghdad.

Salim Shakir said he was walking toward his house in the area when he was hit with shrapnel in the stomach and legs.

“We are shocked because we thought that the violent days had ended,” the 47-year-old taxi driver said from his hospital bed. “This explosion shows that the insurgents are still active, and much is needed to stop them.”

The U.S. military has said the terror network is on the run but retains the ability to conduct its trademark high-profile car bombings and suicide attacks. American and Iraqi troops have faced relatively little resistance since launching the offensive on May 10, but commanders warn that many key insurgent leaders have fled to outlying areas and are planning future attacks.

Yesterday, the attacker detonated his explosives-laden car about 8 p.m. as he approached a checkpoint allowing cars through concrete blast barriers surrounding the headquarters, located in a busy commercial district.

Those killed included five policemen and four civilians, while 46 other people were wounded, according to a police officer, who spoke on condition of anonymity because he wasn’t authorized to release the information.

The blast highlighted the fragility of recent security gains even as the Iraqi government struggles to take advantage of the relative calm in the country to make political progress.