BAGHDAD (AP) – U.S. soldiers killed two Iraqi policemen Saturday after coming under fire during an operation against al-Qaida in northern Iraq, the U.S. military said.

An Iraqi officer confirmed the incident, which occurred near the northern city of Mosul, but said the policemen were manning a checkpoint when they were gunned down.

A U.S. statement said the incident began when U.S. soldiers entered a neighborhood looking for a suspected al-Qaida operative who was believed to be in a building.

The Americans called for the building’s occupants to surrender when they came under fire from another building about 100 yards (meters) away, the statement added. “Despite multiple attempts to identify themselves, the (U.S.) force continued to receive hostile fire. Acting in self defense, coalition forces returned fire,” the statement said.

“Coalition force members immediately moved to the building and linked up with the Iraqi police forces. A search of the building revealed two Iraqi police, who were not in uniform, were killed during the exchange,” the statement added.

The U.S. expressed regret for the policemen’s deaths. Iraqi army Col. Safaa Abdul-Razaq, a regional military spokesman, said the policemen were manning a checkpoint when they were killed by the Americans, but details of the incident remained unclear.

Since the U.S.-Iraq security agreement went into effect Jan. 1, U.S. forces are supposed to coordinate operations with the Iraqis. U.S. troops must obtain warrants from an Iraqi judge before raiding homes in search of extremists.