A female suicide bomber blew herself up among policemen outside a restaurant north of Baghdad on Sunday, killing 15 people and wounding 35, Iraqi police said.
The attack took place in Baquba, capital of multi-ethnic Diyala province, where Sunni Islamist al Qaeda militants have sought to sow tension despite a succession of military offensives that have put the group on the back foot.
Police said the woman walked over to a group of policemen outside a restaurant then detonated explosives under her clothing. Several cars were set on fire.
"When she approached the police patrol, a powerful blast ripped through the area," said Adnan Fayadh, a photocopy shop owner who was nearby.
Police and the U.S. military said 15 people were killed in the attack, which was also near a number of government buildings in Baquba, 65 km (40 miles) north of Baghdad. The U.S. military said the dead included seven policemen.
At a hospital morgue, white sheets covered most of the dead. A man wailed over a body lying on a stretcher.
The U.S. military said 21 female suicide bombers had carried out attacks this year. Most have been in Diyala and Baghdad.
Security officials have blamed those bombings on al Qaeda, which they say has sought to recruit women because they can sometimes escape strict security checks on men.
Violence in Iraq has dropped to a four-year low, but Sunday's bombing was the second big attack in the past week.
U.S. forces have blamed a rogue Shi'ite militia group for a truck bomb that killed 63 people in Baghdad last Tuesday. That was the deadliest attack in Baghdad in more than three months.
U.S. officials accuse al Qaeda insurgents of carrying out scores of large-scale bombings, killing thousands of people in Iraq in the past few years.
A sustained military campaign against al Qaeda has pushed the group out of its traditional strongholds in Anbar province in the west and parts of Baghdad in the past year.
One region where al Qaeda forces regrouped was in the northern city of Mosul, described by the U.S. military as al Qaeda's last major urban stronghold.
Iraqi security officials say al Qaeda's network has been broken in Mosul following an offensive there, Reuters reported.