A truck bomber attacked a revered Shiite shrine in the heart of Baghdad on Tuesday, killing at least 87 people and wounding more than 200 in a resumption of Iraq's relentless sectarian slaughter. The mosque's turquoise dome survived, but the blast buried some worshippers and badly burned others.

Northeast of the capital, a force of 10,000 U.S. soldiers firing artillery and using heavily armored Stryker and Bradley Fighting Vehicles fought their way through western Baqouba and other Al Qaeda sanctuaries in Diyala province. U.S. helicopters and jet fighters flew cover.

In all, 151 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.

The Pentagon is required to issue an initial assessment of the operation next month, and Gen. David Petraeus, the top U.S. commander in Iraq, will report in September. The Democratic-controlled Congress set those reporting deadlines to pressure the White House and American military leadership to make quick progress in curbing violence here so U.S. troops — now 155,000 — can be pulled away from the increasingly unpopular war.

American commanders have said there will be positive results by September but that any return to normalcy requires years. President Bush has even spoken of the U.S. mission in Iraq in terms of the 50-plus-year American troop presence in South Korea.

Tuesday's bombing was a setback. It 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 bombing was presumed to have been carried out by a Sunni attacker because the target was a Shiite mosque. The Khulani mosque's imam, Sheik Saleh al-Haidari, said 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.

Karim Abdullah, the 35-year-old owner of a nearby clothing store, said he was on his way to pray at the mosque when the explosion caused his motorcycle to wobble under him.

"I stopped in shock as I saw the smoke and people on the ground. I saw two or three men in flames as they were getting out of their car," he said.

AP reporters said gunfire rattled through the district after police said the truck exploded in a parking lot near the mosque. A courtyard wall collapsed, and a building just inside the mosque compound was turned to rubble. The mosque sanctuary was slightly damaged.

The Khulani mosque is named after 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. Authorities on Tuesday had reported at least 78 killed in the attack.

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. It was impossible to reconcile the difference in the police and military accounts about the truck's cargo, or whether the bombing involved a parked truck or a suicide driver.

Six of those killed lived in a house behind the mosque, a police official said. Twenty cars were incinerated and 25 shops damaged.

The U.S. military operation in Diyala province, an Al Qaeda bastion, matched in size the force that American generals sent against the insurgent-held city of Fallujah 2 1/2 years ago. The operation began Monday, and by late Tuesday the military had reported only one American death, a Task Force Lightning soldier killed by an explosion near his vehicle. Two soldiers were wounded.

A second soldier from the 3rd Infantry Division died in a roadside bombing south of Baghdad on Monday, the military said in a second statement. Three were wounded in that attack. Earlier Tuesday, the military said a soldier was killed by small arms fire during combat in eastern Baghdad on Monday.

The deaths brought to at least 3,530 the number of U.S. military personnel who have died since the beginning of the Iraq war in March 2003, according to an AP count.

Additionally, Iraqi forces — about 5,000 Iraqi soldiers and 2,000 paramilitary police — joined the battle in Diyala province, according to Mohammed al-Askari, the defense ministry spokesman.

The U.S. commander in the region, Maj. Gen. Benjamin Mixon, said a combined U.S.-Iraqi force of about 3,500 soldiers and police were operating in Baqouba proper, a city of about 300,000.

"We began last night with large-scale air assaults moving by helicopter to surprise the enemy with a large ground assault before daylight. We've had initial good success. ... There's a lot of work left to be done," he told the media.

The military said at least 22 militants had been killed by daybreak.

In southern Iraq, police and hospital officials said the death toll reached 35 in clashes that continued into a second day between Mahdi Army fighters and Iraqi security forces in Nasiriyah, about 200 miles southeast of Baghdad.

Authorities said about 150 people were wounded. They declined to be identified because they feared retribution. Most of the casualties were police or militiamen. A delegation from radical Shiite cleric Muqtada al-Sadr's office arrived in the city to try to end the fighting, according to the city council.

A curfew was imposed on Nasiriyah on Monday, and remained in effect.

At sundown Tuesday in Baghdad, militants fired a volley of mortars into the U.S.-guarded Green Zone. Five crashed to earth near the office of Prime Minister Nouri al-Maliki and one slammed into a structure adjacent to the American post exchange store.

No casualties were immediately reported. The American Embassy confirmed that the Green Zone had been hit by mortar or rocket fire but provided no details.

Complete coverage is available in FOXNews.com's Iraq Center.