BAGHDAD — A female suicide bomber concealing explosives beneath her black robe struck outside a government complex northeast of Baghdad on Sunday, killing at least 15 people and wounding more than 40, U.S. and Iraqi officials said.

It was the 21st suicide mission carried out by a woman in Iraq this year, the U.S. military said, as al-Qaida and other Sunni militant groups try to regroup from major losses suffered at the hands of U.S. and Iraqi forces.

The blast occurred about 1 p.m. as dozens of people were leaving a walled compound that includes a courthouse and the provincial governor’s office in Baqouba, capital of Diyala province and a former al-Qaida in Iraq stronghold 35 miles northeast of Baghdad.