BAGHDAD — A suicide bomber killed an Iraqi police chief and two other officers Thursday as they surveyed the site of the wreckage of a blast a day earlier that devastated a predominantly Sunni neighborhood in the volatile northern city of Mosul.

The casualty toll from Wednesday’s explosion rose to at least 34 dead and 224 injured, said Hisham al-Hamdani, the head of the Ninevah provincial council. The blast obliterated a three-story apartment building and ravaged adjacent houses just minutes after the Iraqi army arrived to investigate tips about a weapons cache.

Brig. Gen. Salah Mohammed al-Jubouri, the police chief for surrounding Ninevah province, was killed as he left the blast site after being confronted by an angry crowd shouting “Allahu Akbar” or “God is Great” while he inspected damage near the crater.

Mosul, 225 miles northwest of Baghdad, has become one of the latest fronts in U.S.-led efforts to rid the country of al-Qaida-linked militants who fled crackdowns in the capital and surrounding areas. While the levels of violence have fallen in much of the country, attacks have persisted north of Baghdad.

In Thursday’s attack, a bomber disguised as a policeman blew himself up as the entourage was just yards away from their vehicles, said police spokesman Saeed al-Jubouri. Al-Jubouri is a tribal name common in Mosul.

The police chief was killed, along with two other officers, and five people were wounded, including three Iraqi police, an Iraqi soldier and a U.S. soldier, the U.S. military said.

The military said initial reports indicated al-Qaida in Iraq was behind Thursday’s attack, but Wednesday’s explosion remained under investigation.

Ahmed Ibrahim, a 40-year-old tailor, said he went to the area early Thursday to check on his shop and found the building intact. But others were not so fortunate, finding entire blocks reduced to rubble and a massive crater at least 30 feet deep where the apartment building used to stand.

“The building that exploded has disappeared while the houses next to it were leveled. Other houses farther away were damaged,” Ibrahim said.

“When I stood near the leveled houses, I heard the voices of people calling for help from under the debris. I went to the firefighters and told them about the voices,” he said. “Some relatives were searching among the debris for their missing relatives. The whole thing is a disaster.”

On Sunday, U.S. military spokesman Rear Adm. Gregory Smith said the military had largely chased al-Qaida in Iraq out of all major urban centers except Mosul, the country’s third largest city and a major transportation hub with highways leading west to Syria and south to Baghdad.

“Mosul will continue to be a center of influence for, a center of gravity for al-Qaida because of its key network of facilitation — both financing and foreign fighters,” he said. “The flow to Mosul is critical for al-Qaida in Iraq.”

Provincial Gov. Duraid Kashmola imposed an indefinite curfew starting at noon Thursday in the city following the attack.

He said a preliminary investigation showed al-Qaida in Iraq was behind Wednesday’s explosion in a bid “to terrorize Mosul residents.”

Wednesday’s explosion came after the Iraqi army received calls that insurgents were using the vacant building as a shelter and a bomb-making factory, police said.

Clashes erupted for about two hours Thursday on the outskirts of Samarra, 60 miles north of Baghdad, between insurgents and members of the local Awakening Council, as the U.S.-allied group is known. A local police officer said two militants were killed.

In other violence, a roadside bomb struck a police patrol in central Baghdad, killing two officers and injuring two, along with three civilians, police said. The explosion was in the predominantly Shiite neighborhood of Karradah.

An explosion also targeted a U.S. patrol in the mainly Shiite northeastern neighborhood of Ur but killed one civilian and wounded two others.