A suicide bomber detonated an explosive-rigged car outside Iraq's main religious affairs office for Shiite Muslims on Monday, shearing off the facade of the three-story building and killing at least 23 people in the deadliest single attack in the country in three months, officials said.

More than 70 people were wounded in the explosion that shattered nearby windows and damaged cars in Baghdad's central Bab al-Muadham area, two police officials said. Firefighters searched the debris for survivors.

In apparent retaliation, a mortar shell hit close to Iraq's main office for Sunni Muslim religious affairs in northeastern Baghdad later Monday, but caused no damage or injuries.

Violence has dropped sharply in Iraq in recent years, but attacks on government offices and members of the security forces, aimed at undermining the Shiite-led ruling coalition, are still common. Monday's explosion came at a time of a prolonged political paralysis caused by sectarian tensions.