BAGHDAD (AP) – Days after the U.S. officially ended combat operations and touted Iraq’s ability to defend itself, American troops found themselves battling heavily armed militants assaulting an Iraqi military headquarters in the center of Baghdad on Sunday. The fighting killed 12 people and wounded dozens.

It was the first exchange of fire involving U.S. troops in Baghdad since the Aug. 31 deadline for formally ending the combat mission, and it showed that American troops remaining in the country are still being drawn into the fighting. The attack also made plain the kind of lapses in security that have left Iraqis wary of the U.S. drawdown and distrustful of the ability of Iraqi forces now taking up ultimate responsibility for protecting the country.

Sunday’s hour-long assault was the second in as many weeks on the facility, the headquarters for the Iraqi Army’s 11th Division, pointing to the failure of Iraqi forces to plug even the most obvious holes in their security. Two of the four attackers even managed to fight their way inside the compound and were only killed after running out of ammunition and detonating explosives belts they were wearing.

The American troops who joined the fight and provided cover fire for Iraqi soldiers pursuing the attackers were based at the compound to train Iraqi forces, said U.S. military spokesman Lt. Col. Eric Bloom. Iraqi forces also requested help from U.S. helicopters, drones and explosives experts, he said. No American troops were hurt, Bloom said.

Under an agreement between the two countries, Iraq can still call on American forces to assist in combat and U.S. troops can defend themselves if attacked. Baghdad has been on high alert since President Barack Obama declared the official end to U.S. combat operations on Wednesday, setting up more checkpoints, intensifying searches of people and vehicles and handing out more guns and bullets to troops guarding the capital.

Well, that didn’t take long.