BAGHDAD — A truck bomb struck a Shiite mosque today in central Baghdad, killing 75 people and wounding more than 200, even as about 10,000 U.S. soldiers northeast of the capital used heavily armored Stryker and Bradley fighting vehicles to battle their way into an al-Qaida sanctuary.

The troops, under cover of attack helicopters, killed at least 22 insurgents in the offensive, the U.S. military said.

The thunderous explosion at the Khillani mosque in the capital's commercial area of Sinak sent smoke billowing over concrete buildings. On Sunday, officials lifted a curfew aimed at preventing retaliatory violence after last week's bombing of a Shiite mosque in Samarra.

Gunfire erupted shortly after the blast.

A police officer, who spoke on condition of anonymity because of security concerns, said the car that exploded was parked in a lot near the mosque and it damaged the outer wall of the building.

Police and hospital officials said at least 75 people were killed and 204 were wounded, adding that the toll could rise as bodies were pulled from the debris.

The mosque's imam, Sheik Saleh al-Haidari, said it was a truck bomb and the explosion hit worshippers as they were leaving afternoon prayers.

"This attack was planned and carried out by sick souls, damaging the mosque's outer wall and collapsing my office and the room above it," al-Haidari told The Associated Press by telephone.

The raids, dubbed "Operation Arrowhead Ripper," took place in Baqouba, the capital of Diyala province, and involved air assaults under the cover of darkness, the military said. The operation was still in its opening stages, it said.

The commander of Iraqi military operations in Diyala, Maj. Gen. Abdul-Karim al-Rubaie, said handcuffs, swords and electricity cables — apparently used as torture implements — had been seized from militant safe houses in the area.

The operation was part of new U.S. and Iraqi attacks on Baghdad's northern and southern flanks, which military officials said were aimed at clearing out Sunni insurgents, al-Qaida fighters and Shiite militiamen who had fled the capital and Anbar during a four-month-old security operation.