Baghdad ? The young applicants gathered early Tuesday outside a police station northeast of Baghdad to find out who had clinched a coveted job on the force. But they were not the only ones who knew this was the day the selection would be made.

Shortly after 8:30 a.m., a woman shrouded in black appeared among the more than 200 men milling outside the concrete blast walls of the station in Muqdadiya. Before anyone could question her, she detonated the explosives hidden under her gown, killing as many as 19 people and injuring 33, police and witnesses said.

As the smoke and dust settled, a horrific scene was revealed: writhing bodies, severed limbs and charred, bloodied survivors screaming on the ground.

No one immediately claimed responsibility for the attack in the mostly Sunni town, a rare case of a bombing carried out by a woman. It also came at a time of growing friction within the embattled minority that dominated Iraq under Saddam Hussein.

A number of Sunni Arab clans and local insurgent groups have turned against the militants of al-Qaida in Iraq, whom they once harbored, accusing the foreign-dominated network of indiscriminate attacks against Iraqi civilians. Sunnis are joining the police in areas where they once refused to cooperate with the Iraqi government.

As the toll of Tuesday’s attack sank in, survivors expressed outrage that they had been left standing outside a police station that is the target of frequent mortar and rocket attacks, was overrun once by insurgents and already was targeted by one suicide bomber.

The dead were among at least 55 Iraqis reported killed in violence Tuesday. In Baghdad, U.S. attack helicopters blasted gunmen holed up inside buildings in some of the most intense fighting in the city since the start of a security crackdown nearly two months ago. At least 13 people were killed and dozens wounded, including 16 U.S. soldiers.