In this photo provided by the Mecklenburg County Sheriff's Office, Steven D. Green is shown in A booking mug shot at the Mecklenburg County jail in Charlotte, North Carolina, Monday, July 3, 2006. [AP]

Iraq's prime minister Wednesday demanded an independent inquiry of the rape-slaying of a girl and the killing of her family, saying the immunity from Iraqi prosecution enjoyed by US forces "encouraged them to commit such crimes."

A suicide car bomb targeting Iranian pilgrims struck near a Shiite shrine in the holy city of Kufa on Thursday, killing at least 12 people and wounding 37, police said.

Police at the scene said the attacker was driving a minivan behind two buses carrying the pilgrims and detonated his explosives as they were deboarding near the shrine of Maitham al-Tamar, a follower of Imam Ali, and not far from the Kufa mosque.

Nobody claimed responsibility for the attack, but suspicion immediately fell on Sunni extremists amid rising sectarian tensions in the country.

"We denounce this act targeting innocent people and pilgrims," an aide to radical cleric Muqtada al-Sadr, Sahib al-Amiri, said. "It was meant to shake the stability in Najaf."

Kufa and its twin city Najaf, 100 miles south of Baghdad, are in a relatively peaceful area of Iraq, tightly controlled by police and Shiite guards, and such attacks have been rare.

Prime Minister Nouri al-Maliki, whose brief tenure has been marked by several high-profile allegations of abuse by US forces, called for an Iraqi investigation, or at least a joint inquiry, into the March 12 rape and murder of Abeer Qassim Hamza, and the killing of her mother, father and sister at their home in Mahmoudiya, south of Baghdad.

He also said the agreements under which US-led coalition troops enjoy immunity from prosecution by Iraqi courts should be reviewed.

"We believe that the immunity given to members of coalition forces encouraged them to commit such crimes in cold blood (and) that makes it necessary to review it," al-Maliki told reporters in Kuwait.

Al-Maliki spoke two days after former Army Pfc. Steve D. Green was charged in federal court in Charlotte, North Carolina, with rape and four counts of murder. Green was held without bond. At least four other US soldiers still in Iraq are under investigation in the attack, which occurred near the town of Mahmoudiya.

In Baghdad, an American military spokesman stressed that the US command was taking the allegations seriously and would discuss al-Maliki's demands when he returns from a tour of Persian Gulf countries.

"We are here as guests of the Iraqi government. They are a sovereign nation," Maj. Gen. William Caldwell said. "When the prime minister gets back, the coalition will engage with him and discuss what he wants to discuss."

Green and the four others were members of the same unit as two soldiers whose mutilated bodies were found June 19, three days after they were abducted by insurgents in Youssifiyah. A third soldier was killed before the others were abducted.

But Caldwell said investigators had found nothing to indicate the June killings were retaliation for the rape-slaying. "It appears they're very separate and distinct events that occurred, from what we've been able to find thus far," he said, adding the ongoing questioning of some 20 "persons of interest" has yielded no information that would link the two incidents.

Both events, however, raised questions about procedures within the unit, which is part of the 101st Airborne Division but currently attached to the 4th Infantry Division. US officials had said they were investigating how the three slain soldiers were left alone last month in an al-Qaida-infested area.

The alleged rape-slaying occurred after the soldiers left a checkpoint for the victims' house, according to court documents.

In Mahmoudiya, Abeer's uncle said the family thought insurgents had been responsible until the US military announced an investigation last week.

"Nobody knew who killed them," Ahmed Taha told AP Television News. "Some said it was insurgents, and in fact, we ruled out the American troops."

After the US announcement, some neighbors told him of seeing US soldiers in the area at the time of the attack but said they had been too afraid to come forward at the time.

"They were afraid of telling the truth, really, we were surprised by this news," Taha said, wearing a black checkered keffiyah as he stood near mounds of dirt and stone markers where the family of four was buried.

Taha said he arrived at the scene about four hours after the killings and found the charred body of his 15-year-old niece, along with those of her mother, Fikhriya Taha, her father, Qassim Hamza, and her younger sister, Hadeel Qassim Hamza. Taha said the mother and father had been shot four times and showed signs of having been beaten.

Abeer's 8-year-old brother, Ahmed Qassim, said he and his brother found the bodies when they came home from school.

"We found them dead in the house. We also found the house blackened and smoke coming from it," Ahmed said, holding a shovel and sitting near a mud puddle with a cow grazing behind him.

The allegations emerged as al-Maliki's new national unity government was trying to promote a reconciliation plan to end the unrest.

At least 24 people were killed Wednesday in attacks nationwide, including six who died in a a car bombing outside a Sunni mosque in a mostly Shiite area of northwestern Baghdad. Fourteen others were wounded in that attack, police said.

Elsewhere, a suicide car bomber struck a new police station in Mosul, killing at least one person and wounding seven. Gunmen also killed a teacher near his home in eastern Mosul, and a barber shop was ambushed northeast of Baghdad, killing two civilians including the owner.

Caldwell predicted an increase in vehicle bombings now that Abu Hamza al-Muhajer, also known as Abu Ayyub al-Masri, has succeeded the late Abu Musab al-Zarqawi as head of al-Qaida in Iraq. Al-Masri'd specialty is car bombs, the general said.

"I think it would only be prudent for us to expect to see a rise in vehicle-borne improvised explosive devices ... given his specialty and background and training that we've seen that he's used," Caldwell said.

The US military reported 74 car bombs in the four weeks ending June 9, two days after al-Zarqawi was killed, compared with 125 in the four weeks since that date.

Meanwhile, Vice President Tariq al-Hashimi said a group claiming to have kidnapped a Sunni legislator made several demands for her freedom: the release of all detainees, a timetable for the withdrawal of foreign troops and an end to attacks on Shiite mosques.

Al-Hashimi said the group contacted his Iraqi Islamic Party, but did not offer proof that it was holding lawmaker Tayseer al-Mashhadani. He said he believed she was still alive.

Al-Mashhadani and seven of her bodyguards were seized Saturday by gunmen at a checkpoint in a Shiite part of eastern Baghdad. The main Sunni political alliance has suspended its participation in parliament to demand her release.

"We call on you in the name of Islam to end her suffering," al-Hashimi said in a message to the kidnappers.