A roadside bomb killed a prominent member of Muqtada al-Sadr's political movement Thursday, raising fears of new internal Shiite bloodshed ahead of regional elections expected in January.

The victim's allies blamed U.S. and Iraqi forces for the blast, which occurred near an Iraqi army checkpoint in mostly Shiite eastern Baghdad. Suspicion also fell on Shiite splinter groups — some with suspected links to Iran, which has sheltered al-Sadr for nearly 18 months.

Saleh al-Auqaeili, considered a moderate within al-Sadr's movement, was traveling in a convoy with other Shiite lawmakers when the blast occurred about 200 yards from the Iraqi army checkpoint, a colleague said.

Al-Auqaeili was rushed to the hospital where he later died of his wounds, Sadrist spokesman Ahmed al-Massoudi said. One commuter on a motorcycle was also killed in the blast, police said.

Al-Sadr's followers have long opposed the U.S. military presence in Iraq, and some of them were quick to blame the Americans and their Iraqi allies, citing the movement's opposition to a U.S.-Iraqi security agreement that has been under negotiation for months.

"The occupation forces sent us a message by staging this attack because of our stance against the agreement," said al-Massoudi, the Sadrist spokesman.

Later, however, the Sadrist political department called the killing a "terrorist act of criminal gangs," a phrase often used to describe renegade Shiite militants that the U.S. believes are trained and armed by Iran. Tehran denies links to Iraqi Shiite militants.

Maj. Mark Cheadle, a spokesman for the U.S. military's Baghdad command, said the attack appeared to have been carried out by "unaligned" Shiite groups.

Police detained 14 people for questioning, including 12 members of a government-run security force that protects a power station near the blast site.

The attack reflects tension within the Shiite community following the splintering of al-Sadr's Mahdi Army militia, which fought U.S. and Iraqi troops for weeks in Baghdad's Sadr City district until a cease-fire last May.

Shiite politicians negotiated the truce that enabled the Iraqi army to take control of the sprawling Sadr City slum that had been al-Sadr's stronghold in the capital for years.

But some militia fighters were angered at what they considered a "sell-out" by Shiite politicians and refused to heed al-Sadr's orders transforming the Mahdi militia into an unarmed social movement.

U.S. and Iraqi officials also fear a rise in violence ahead of provincial elections due by Jan. 31. Much of the concern has focused on regional contests in the heavily Shiite south, where parties in the government of Prime Minister Nouri al-Maliki face a strong challenge from al-Sadr's followers in a region that includes vast oil wealth and prestigious religious shrines.

The U.S. commander in charge of southern Iraq warned Thursday that he expects "nefarious" Iranian meddling in the provincial balloting — including bombings and "assassinating prominent candidates" as the elections approach. His comments were not linked to the al-Auqaeili killing.

"There's no doubt that Iran influences Iraq," Maj. Gen. Michael Oates told reporters. "The risk would come if they seek to influence the election using some nefarious operations or surrogates or they raise the level of violence in the country."

Several followers of al-Sadr have been targeted in past attacks, but Thursday's bombing was notable because it occurred in an area that is considered relatively secure and within view of an Iraqi army checkpoint.

Falah Hassan Shanshal, who was traveling in a different car in the same convoy, said the group became suspicious when it discovered there were no traffic jams in the usually crowded area. He said the "operation was a pre-planned one" and that the explosion was remote-controlled.

"We hold the security forces responsible for this attack. They should be responsible for the security of the city," he said.

Also Thursday, a U.S.-allied Sunni militia leader was killed with three of his relatives when a roadside bomb exploded next to a pickup truck in which they were traveling in Udaim, north of Baghdad, police said.

Iraqi police also reported that bombs struck houses of people who had recently returned to their religiously mixed neighborhoods south of Baghdad, killing nine people.

One of the blasts killed a Sunni Muslim couple and their three children on Wednesday in Madain. The second attack killed four members of a Shiite family in Baghdad's Wahda district the same day, the officials said, speaking on condition of anonymity because they weren't authorized to release the information.

A wave of brutal sectarian violence drove many Sunnis and Shiites to flee homes in neighborhoods where the two sects were mixed and take refuge in areas where one sect or the other dominates. With the easing of sectarian violence over the past year, some have tried to return to their original homes.