BAGHDAD — An explosives-rigged bicycle parked near a military truck killed two civilians at a market outside Baghdad on Tuesday, and a member of a Sunni group allied with U.S. forces was killed in the capital by a bomb concealed on his car.

The death late Monday of the Sunni — a member of one of the groups of fighters that have turned against al-Qaida in Iraq and allied with the United States — was the second in two days in Baghdad. On Sunday, another Sunni leader was killed when his booby-trapped car exploded.

The violence came as David Petraeus, the American general credited with helping to pull Iraq back from the brink of all-out civil war, handed over his command to his successor.

The bicycle was left near an Iraqi military truck parked at the main market in Taji, 12 miles north of Baghdad, according to a police officer who spoke on condition of anonymity because he was not authorized to speak to the media.

The soldiers from the truck were patrolling the market on foot when the blast went off.

Meanwhile, in the Shiite enclave of Sadr City in Baghdad, about 2,000 residents demonstrated Tuesday against the visit to Iraq by U.S. Defense Secretary Robert Gates, who attended the handover ceremony.

The protesters carried Iraqi flags and images of anti-U.S. cleric Muqtada al-Sadr, chanting: "Down, down U.S.A."

Earlier this year, Iraq's U.S.-backed government launched a crackdown on al-Sadr's Mahdi Army militia in Baghdad and southern Iraq, severely weakened it. However, al-Sadr retains a strong political following among disadvantaged Shiites who feel the mainstream Shiite parties have failed to improve their lives.

Despite the security gains, insurgents retain the ability to carry out devastating attacks. On Monday evening, a female suicide bomber blew herself up among a group of police officers northeast of Baghdad, killing at least 22 people. Hours earlier, car bombs in the capital killed 13 people.

Police and soldiers were heavily deployed in Balad Ruz, the town in Diyala province where the suicide bomber struck on Monday. Even so, a roadside bomb killed one soldier and injured another in the town on Tuesday morning, the Iraqi military said.

Authorities imposed a vehicle ban until further notice, a police official said. He spoke also on condition of anonymity because he wasn't authorized to speak to the press.

Also Tuesday, the Health Ministry said it has confirmed 77 cases of cholera since late August.

The cholera outbreak, which has killed five people, has spread in part due to a lack of clean drinking water — a problem worsened by the poor state of infrastructure after years of deprivation and war.