BAGHDAD — Three suicide bombers attacked Iraq’s federal police headquarters in Mosul today, leveling the building and killing the top police commander there, a prominent figure who had toiled to rid the northern city of al-Qaida militants, and who had escaped past assassination attempts, officials said.

While violence has subsided significantly in Iraq in the past years, insurgents frequently target the country’s government institutions and security forces in an effort to destabilize the U.S.-backed Iraqi authorities as American troops prepare to leave by the end of next year.

The attack in Mosul, a former al-Qaida stronghold, began when three men with explosives vests slipped through an opening in the blast walls surrounding the compound housing Iraq’s 1st Battalion of the National Police, police said.

Police shot one of the attackers in an open-air yard, and his vest exploded — but under cover of the blast, the other suicide bombers charged into the headquarters building.

One of the bombers entered the ground floor office of the battalion’s commander, Lt. Col. Shamil al-Jabouri, where he was sleeping, and blew himself up, killing al-Jabouri instantly, a police officer at the scene said.

The other bomber detonated his explosives-laden vest on the ground floor of the building shortly after the first blast, police said.

The powerful twin explosions brought the whole building down, burying the slain commander and possibly others under the rubble, police said.