A suicide bomber driving a minibus pulled alongside a convoy of elite Iraqi commandos in the capital Sunday and detonated his explosives, killing 10 people in a spray of burning metal, witnesses said.

The powerful explosion rattled windows miles from the stretch of highway in the eastern neighborhood of Ghadeer. Blood from the dead and injured soaked bread in roadside stalls.

Hours later, Ahmed Dawood, 25, a trader who was driving on the highway at the time and witnessed the explosion, was still shuffling around in shock, carefully stepping over sandals and pieces of flesh.

"The highway was so crowded," said Dawood, dazed but uninjured. "When the explosion happened, I searched for a place to hide because there was heavy shooting."

Iraqi officials provided no immediate count of the casualties. Witnesses said they saw at least 10 charred bodies, the majority of whom were commandos, part of a highly trained Interior Ministry protection force. Unlike U.S. forces in Iraq, who travel in armored vehicles, the commandos were riding in the back of a pickup truck.

[On Monday, a suicide bomber rammed his car into a bus carrying Oil Ministry employees outside the ministry office, killing at least six people and wounded 14, police and Interior Ministry sources told the Reuters news agency.]

Six people were also killed Sunday morning in Sadr City, a large Shiite slum in Baghdad, when U.S. forces and Iraqi commandos exchanged gunfire with members of the Mahdi Army, a militia loyal to the popular Shiite cleric, Moqtada Sadr.

The Mahdi Army controls Sadr City, which has become one of the safest areas of the capital in recent months. Residents of the slum stroll the streets after dark, taking in the cooler night air when the power goes out -- an activity unheard of in other parts of Baghdad.

The U.S. military said it had no immediate information on the incident.

Maj. Gen. Raad Tamimi, an Interior Ministry official, said the clashes began when an armed group of Sadr's followers gathered near a mosque, raising the suspicions of U.S. and Iraqi troops on patrol there. The U.S. forces "ordered the armed men to withdraw, but they refused and moved toward them," prompting the Americans to shoot, Tamimi said.

But residents of Sadr City said that the Iraqi troops had joined the Americans in an unprovoked assault on the Mahdi Army members.

Waleed Wadi Lafta, a resident who said he witnessed the exchange of gunfire, said "there were six pickups of the Interior Ministry commandos" and six American Humvees. "They came to arrest a man whom they did not find."

The U.S. and Iraqi forces then "started shooting randomly at the people who were in the street," he said. "They shot at the mosque and the nearby shops."

The gate of the mosque was riddled with bullet holes, but it was not possible to independently confirm how or when it was damaged. The tall, spiraling minaret of the mosque was also pocked with bullet holes.

Crowds gathered in front of the mosque cursed what they called the "occupation" and the government.

"If the government cares about us, they should not send others to kill us," said Mohammed Sabah, 23, a high school teacher and resident of Sadr City.

In the Shiite holy city of Najaf, 90 miles south of Baghdad, Sayyid Riyadh Nouri, a senior aide to Sadr, said that the cleric had asked people not to retaliate. "Our leader, Sayyid Moqtada Sadr, ordered the people to be in the highest self-control and not to be engaged in any military fighting," he said.

Nouri called for immediate government intervention "to stop this crisis that will lead to the instability in the country."

Meanwhile, a U.S. soldier was killed Sunday when his vehicle rolled over during a patrol in western Iraq, the military said. Two other soldiers were injured in the accident in Trebil, near the border with Jordan, according to the Associated Press. No further details were available.

In Hilla, 55 miles south of Baghdad, five Iraqi civilians were killed and 49 were injured when a booby-trapped bicycle exploded in front of an ice-cream parlor and juice bar in the center of the city, said Capt. Muthanna Ahmed, a press officer at the Babil province police directorate. He said many of the injured were in critical condition.

At Hilla's General Hospital, Hadi Alwan, 36, who was among the injured, said the area was crowded with people when the explosion happened. "I did not remember anything, except my legs were bleeding and then I fainted," he said.

Maj. Gen. Qais Hamza, police chief for the province, ordered the hospital to prevent injured patients from leaving because police suspected that the bomber might be among them.

In Samarra, about 65 miles north of Baghdad, armed men shot and killed five Iraqi security guards employed by the Northern Oil Co., police Lt. Raed Mahdi said. In the same area, the bodies of three unidentified people who had been shot were found in the Tigris River, Mahdi said.

Iraqi and U.S. officials have warned of escalating violence before the Oct. 15 national referendum on a new constitution, an issue that has divided Sunni and Shiite Muslim political parties. The Shiites, who make up the vast majority of the population, largely support the constitution, which would give them a degree of autonomy under a new federalist system. The Sunnis, who lost political control after president Saddam Hussein was ousted in 2003, have voiced opposition to the document. Sunnis make up about 20 percent of the population.

Thousands of people demonstrated against the constitution Sunday in Ramadi, a city west of Baghdad in the Sunni Triangle. The protesters -- students, religious leaders and government employees -- also denounced insurgents for threatening people who choose to go to the polls.

Special correspondent Saad Sarhan in Hilla and Salih Saif Aldin in Samarra contributed to this report.

Iraqis carry the coffin of one of six people killed when U.S. and Iraqi forces clashed outside a mosque in Baghdad's Sadr City slum with gunmen loyal to the Shiite Muslim cleric Moqtada Sadr.An Iraqi boy cries for his uncle, who was among those killed in clashes in Sadr City. The neighborhood had recently become one of Baghdad's safest.