A homicide car bomber struck an Interior Ministry convoy in Baghdad (search) on Sunday, killing seven police commandos and two civilians. Earlier, a bomb mounted on a bicycle blew apart a music store in Hillah, south of the capital, killing one, officials said.

In the early morning, U.S. and Iraqi forces clashed with gunmen loyal to radical Shiite cleric Muqtada al-Sadr (search), killing at least eight Iraqis in an east Baghdad slum. The clash was certain to heighten tensions between U.S. and Iraqi security forces and followers of al-Sadr, who is building opposition to the country's new constitution, which will be put to voters in an Oct. 15 referendum.

The attack on the three-vehicle convoy of commandos also wounded 19, including at least 11 members of the elite unit, said Capt. Nabil Abdel-Qader (search).

The bombing in Hillah, a mixed Sunni-Shiite city about 60 miles south of Baghdad, wounded 48 people, said Dr. Mazen Abdul-Sada of Hillah General Hospital. Ultraconservative religious figures have deemed some music on sale in the country offensive to their interpretation of Islam.

The fighting in Baghdad's Sadr City, an eastern Shiite slum, erupted before dawn Sunday. Police Maj. Falah al-Mohamadawi said a U.S. patrol came under fire as it entered the district to arrest members of the al-Mahdi Army, the militia loyal to al-Sadr. U.S. forces returned fire, killing at least eight Shiite gunmen and wounding five, he said.

However, Shiite cleric Amer al-Hussainy, a top al-Sadr aide in Baghdad, said only three gunmen were killed. The five other deaths were civilians — including a woman — struck by stray rounds, he said.

U.S. military officials would not say whether fighting occurred in Sadr City. Master Sgt. Greg Kaufman said a joint U.S.-Iraqi patrol came under fire and there were several "engagements" in the area.

"There were some anti-Iraqi forces killed," he said, adding that the number of dead was not known.

The clash introduced another potential obstacle to Shiite unity on the constitution just three weeks before the nationwide referendum.

On Saturday, Abdel-Aziz al-Hakim, the head of the Shiite Supreme Council for the Islamic Revolution in Iraq, told a crowd of about 2,000 supporters that "it is our religious duty to say 'yes' to the constitution and to go to ballot boxes." SCIRI is the most powerful Shiite political organization in Iraq.

Al-Hakim, speaking during a ceremony marking the 1991 Shiite uprising against Saddam Hussein, said militants and former regime supporters were trying to undermine Iraqis' hopes for security.

His appeal came just two days after Shiite Grand Ayatollah Ali al-Sistani also directed his followers to back the charter.

Al-Sistani's endorsement is seen as key to solidifying Shiites support. If two-thirds of voters in any three of Iraq's 18 provinces reject the charter, a new government must be formed and the process of writing a constitution starts over.

Iraq's Sunni Arab minority — which forms the core support network for the country's violent insurgency — has opposed the constitution, pointing specifically to clauses addressing the issue of federalism and Iraq's Arab identity, which they want clearly reflected in the new charter.

Minority Sunni Arabs dominate four provinces and could defeat the new charter as a voting bloc. On Saturday, Sunni clerics and tribal leaders meeting in Jordan for security reasons expressed optimism they could do just that while gathered at a meeting organized to scuttle the charter.

The three-day meeting ended with a communique urging a 'no' vote "if the constitution's main points on Iraq's unity and Arab identity are not rectified, as well as articles related to political and racial segregation."

Al-Sadr, whose al-Mahdi Army has refrained from confrontations with the U.S. military since their last battle in August 2004, also sided with the Sunnis in objecting to the constitution.

Overcoming opposition from al-Sadr is seen as key to securing the necessary votes.

But the task has become increasingly difficult after British forces arrested two al-Mahdi Army officials in the southern city of Basra about a week ago. Militiamen and residents also clashed with British troops days later after two British soldiers were detained by Iraqi authorities.

Britain subsequently launched a raid to free the men, who were disguised as Arabs when they were arrested. The operation heightened tensions in the city, about 340 miles south of Baghdad, and an Iraqi judge issued a homicide warrant for their arrest.

British officials say the warrant is illegal under Iraqi law, and their personnel are immune to prosecution in Iraq.

Prime Minister Tony Blair reaffirmed that position Sunday. When asked by the British Broadcasting Corp. if Britain would accept the warrants, Blair responded: "No."

"We will do whatever is necessary to protect our troops in any situation," Blair said at his governing Labour Party's annual conference in Brighton, England.

The British leader also said he had been surprised by the strength of the insurgency, but he vowed that British forces were not preparing to leave.

"No, I didn't expect quite the same sort of ferocity from every single element in the Middle East that came in and is doing their best to disrupt the political process. But I have absolutely no doubt as to what we should do. We should stick with it," he said.

But Defense Secretary John Reid said British troops could begin handing over their responsibilities to Iraqi soldiers and police next year.

In other developments, the U.S. military disputed an account of an incident in Beiji on Saturday in which Iraqi police said U.S. troops killed eight Iraqis and wounded six others after their patrol was hit by a roadside bomb.

The military said an Iraqi army patrol came under small-arms fire in the area about 155 miles north of Baghdad, and U.S. troops came to their aid.

Two Iraqi army soldiers were wounded in the fighting, and U.S. troops found four Iraqi civilians who were injured, military spokesman Lt. Col. Steven A. Boylan said. It was not known if the injuries "were due to the explosion or the ensuing fight after the firefight," he said.

Elsewhere in Baghdad, Iraqi police said they found five dead bodies in two separate locations. The bodies were bound and had multiple bullet wounds.

In Mosul, gunmen clashed with Iraqi police Sunday morning, leaving two civilians dead and three others wounded in the city 225 miles northwest of Baghdad, said Dr. Baha al-Din al-Bakri of al-Jumhouri hospital.