(CNN) -- At least four police officers were killed Wednesday when two suicide bombers, wearing explosives-packed vests, attacked a police battalion in western Mosul, officials said.
The attackers detonated their vests in the room of Lt. Col. Shamel Ahmed Aughla, who headed the battalion, officials in Baghdad and Mosul said.
Aughla was killed instantly, the officials said, adding that part of the building collapsed in the explosions.
Three other officers also died in the blast, along with the attackers, police said.
A third suicide bomber who tried to enter the building was shot dead by police, officials said.
It was not immediately known whether anyone else was killed or wounded in the attack.
Several officers were unaccounted for after the blast and rescue crews were at the scene late Wednesday morning scouring through the wreckage of the building, looking for them.
Mosul is located in Nineveh province, about 420 kilometers (260 miles) north of Baghdad. The militant group, al Qaeda in Iraq, is still active in some parts of the province .