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-murder of Abeer Qassim Hamza, and the killing of her mother, father and sister at their home in Mahmoudiya, south of Baghdad.

"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, calling for the policies to be reviewed.

Former Army Pfc. Steve D. Green was charged Monday in federal court in Charlotte, N.C., with rape and four counts of murder. He was held without bond. At least four other US soldiers still in Iraq are under investigation in the attack.

In Baghdad, an American military spokesman stressed that the US command was taking the allegations seriously and would discuss al-Maliki's demands.

The attack in Kufa also occurred a day after the US military 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 is an explosives expert specializing in such attacks, Maj. Gen. William 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.

AP Television News footage showed the charred hulks of the buses while a bulldozer cleared the blackened mass of metal that apparently was the minivan used in the attack.

On April 6, a car bomb exploded in Najaf, killing at least 10 people some 300 yards from the Imam Ali shrine on a street that leads to the city's massive cemetery - used by Shiites from throughout the country who come to the city to bury their dead.

Pilgrims traveling to holy sites in the area also have been targeted. Other past attacks included a mortar barrage that hit the Kufa mosque in August 2004, killing 27 people and wounding 63, and a car bomb in Najaf in August 2003 that killed more than 85 people, including Shiite leader Ayatollah Mohammed Baqir al-Hakim.

Attacks on houses of worship have stoked tensions between Shiite and Sunni Muslims, especially after the Feb. 22 bombing of a Shiite shrine in Samarra, an act that triggered reprisal attacks against Sunni mosques and clerics.

The Kufa mosque holds the shrine of Muslim Bin Aqeel, a follower of Imam Hussein, the grandson of the Prophet Muhammad. It also was the site of fierce clashes between al-Sadr's followers and U.S. troops in 2004.

Millions of Shiite Muslim pilgrims from Iran and elsewhere take dangerous bus journeys through Iraq to travel to the shrines in the area. Officials have begun expanding and modernizing the now-shuttered Imam Ali Airport in Najaf in an attempt to provide safer transportation.

In other violence Thursday, according to authorities:

-- A suicide car bomb struck a joint Iraqi-US checkpoint near Ana town, about 150 miles northwest of Baghdad, wounding two Iraqi solders.

-- A former judge during Saddam's regime was killed and his son was wounded in a drive-by shooting in western Baghdad.

-- Gunmen killed a real estate broker at his office in Mosul. A roadside bomb also struck a police patrol in the northern city, wounding one of the policemen.

-- Police found the bodies of six people who had been handcuffed and shot in the head in three different locations in Baghdad.