Thousands of U.S. and Iraqi troops pressed forward for the second day Wednesday with an operation aimed at clearing out a Sunni insurgent stronghold northeast of Baghdad. The U.S. military said at least 30 Al Qaeda fighters were killed and several bombs and weapons caches destroyed as the soldiers fought their way through the streets of Baqouba.

The U.S. military operation that involves some 10,000 American soldiers in Diyala province, an Al Qaeda bastion to the north and east of Baghdad, matched in size the force that American generals sent against the insurgent-held city of Fallujah 2 1/2 years ago. By late Tuesday, the military had reported only one American death, a Task Force Lightning soldier killed by an explosion near his vehicle.

Iraqi forces also have joined the battle in Diyala. Iraqi Defense Ministry spokesman Mohammed al-Askari said about 5,000 Iraqi soldiers and 2,000 paramilitary police were fighting, while the military said about 1,000 Iraqi soldiers and an equal number of police were involved. The differing numbers could not be immediately reconciled.

The Iraqi Defense Ministry said that three civilians had been wounded in Diyala in addition to the 30 Al Qaeda militants. It also said 13 suspected Al Qaeda fighters had been detained and 14 roadside bombs dismantled, along with three car bombs and three weapons caches.

"The citizens received the valiant Iraqi army forces with overwhelming joy as the soldiers were waving to them with the V for victory sign," the ministry said in a statement.

The head of a Sunni insurgent group that has turned against Al Qaeda and is cooperating with U.S. and Iraqi forces in the area said his fighters were participating in the operations and had succeeded in clearing several neighborhoods in eastern and western Baqouba.

The militant leader, who declined to be identified for fear of retribution, spoke as his fighters linked arms, chanted and danced while women ululated in celebration. An Associated Press reporter also saw residents in the Mustafa area in western Baqouba serving food to fighters who had battled al-Qaida and starting to repair their stores.

Sectarian violence persisted to the south, with suspected Shiite militiamen detonating a bomb inside a Sunni mosque in Haswa, 30 miles south of Baghdad, at about 1 a.m., then in another mosque near Hillah, about 60 miles south of the capital, about six hours later, local police officers said, speaking on condition of anonymity because of security concerns.

The attackers near Hillah also targeted the imam's house near the mosque, but the cleric fled when he saw them coming, according to the police.

Meanwhile, gunmen blew up two Sunni mosques south of Baghdad Wednesday in an apparent retaliatory attack a day after a suicide truck bombing devastated a revered Shiite mosque in the heart of the capital, killing at least 87 people. The blasts caused heavy damage but no casualties, police said

Tuesday's bombing against the Khulani mosque in central Baghdad was the deadliest single attack in Iraq since April 18, when at least 127 civilians were killed when a bomb detonated in a parked car at a mostly Shiite market in central Baghdad.

Police said a truck piled high with electric fans and air conditioners delivered the huge bomb at the Khulani mosque. The powerful explosion in the busy commercial district cut deep into Iraq's Shiite community on just the second day after authorities lifted a four-day curfew in the capital.

The vehicle ban had been imposed to prevent revenge attacks after a bombing last week brought down twin golden minarets at the important Shiite al-Askariya shrine in Samarra, north of the capital. A bombing that destroyed the golden dome there on Feb. 26, 2006, set in motion the sectarian bloodletting that has sundered the sectarian fault line in Iraq.

Tuesday's attack bore the hallmarks of Sunni insurgents, particularly Al Qaeda. The Khulani mosque's imam, Sheik Saleh al-Haidari, said the bombing was particularly deadly because worshippers were just leaving a prayer service.

"This attack was planned and carried out by sick souls," al-Haidari told The Associated Press by telephone. He said his office and the room above collapsed but that he was not in the mosque at the time of the attack.

A courtyard wall collapsed, and a building just inside the mosque compound was turned to rubble. The mosque sanctuary was slightly damaged. AP Television News footage showed broken glass scattered on the patterned rugs that lined the floor around the golden tomb that is believed to hold the remains of Sheik Mohammed Othoman Said al-Khulani.

Al-Khulani is a much-revered Shiite figure who, according to the sect's tradition, was one of four "earthly" deputies anointed by the Imam Mohammed al-Mahdi, who disappeared in the 9th century. Shiites believe the so-called "Hidden Imam" will return to Earth to restore justice to humanity.

The Interior Ministry reported Wednesday that the death toll had risen to 87, with another 214 injured in the blast.

Lt. Col. Scott Bleichwehl, a military spokesman in Baghdad, said the truck was loaded with propane tanks and that a suicide driver detonated his bomb when the vehicle became stuck trying to drive over a curb.

Battles also continued south of Baghdad between Iraqi security forces and Shiite militiamen loyal to radical cleric Muqtada al-Sadr.

Four soldiers were killed and a Humvee was burned in nearly two hours of clashes in the Shiite town of Numaniyah, 77 miles southeast of Baghdad, police said. The fighting erupted hours after five other Iraqi soldiers were killed and three were wounded by a roadside bomb in the mainly Sunni town of Madain, on the southeastern outskirts of Baghdad.

Further south, the U.S. military said three militants had been killed, including a senior leader of al-Sadr's Mahdi Army, and 45 detained after two days of clashes in Nasiriyah, about 200 miles southeast of Baghdad. Iraqi police and hospital officials put the casualty toll at 35 killed and 150 wounded.

In all, 142 people were killed or found dead in sectarian violence Tuesday, a toll reflecting carnage associated with the months before the U.S. security crackdown in the capital began Feb. 14.