Gunmen killed an aide to Iraq's most influential Shiite cleric and two bodyguards in a drive-by shooting outside a Baghdad (search) mosque Friday — an attack likely to stoke tensions between the Shiite majority and the Sunni minority, officials said.

Elsewhere in the capital, a car bomb exploded near a checkpoint outside offices of Prime Minister Ibrahim al-Jaafari's Islamic Dawa Party, killing one person and injuring at least four more, officials said. Al-Jaafari (search) was not there at the time, party official Ayad al-Nedawi said.

Shiite cleric Kamal Ezz al-Deen al-Ghuraifi (search), an aide to leading Shiite cleric Grand Ayatollah Ali al-Sistani, was shot as he was about to leave al-Doreen mosque after leading prayers, according to his son, Hamid Kamal. Police Lt. Thair Mahmoud confirmed the attack.

"Gunmen in a speeding car sprayed him with machine guns," Mahmoud said.

Two bodyguards were killed and another four were wounded, he said.

Al-Ghuraifi, in his 60s, had been a Baghdad representative of al-Sistani for the past decade, said Amer al-Hussaini, a friend of al-Ghuraifi's and a member of al-Hawza al-Ilmiyah, the Shiites' ancient seminary in the southern city of Najaf.

It was the third attack on al-Sistani aides in recent weeks.

Last week, gunmen killed Samir al-Baghdadi, who represented al-Sistani in Baghdad's predominantly Shiite al-Amin district. In May, attackers assassinated Shiite cleric Mohammed Tahir al-Allaq, al-Sistani's representative in the Jurf al-Nadaf area near Madain, about 14 miles southeast of Baghdad.

"These attacks are aimed at stoking sectarian tensions between Iraqis," al-Hussaini said.

Separately, five masked gunmen stormed a Sunni mosque in the same neighborhood and kidnapped an imam, Sheik Amer al-Tikriti, during Friday prayers, police 1st Lt. Mohammed al-Hiyani said.

A Sunni-dominated insurgency has killed about 1,380 people — mostly civilians and Iraqi forces — since Prime Minister Ibrahim al-Jaafari announced his Shiite-dominated government April 28.

Islamic extremists, such as Jordanian-born Abu Musab al-Zarqawi and his Al Qaeda in Iraq group, are determined to start a civil war by attacking Iraqi security forces and members of the country's Shiite majority.

In the attack on the Islamic Dawa Party offices in Baghdad's Mansour neighborhood, the homicide bomber detonated the car near a checkpoint about 80 feet from the building, which used to be al-Jaafari's house.

Interior Ministry administrative affairs undersecretary police Maj. Gen. Adnan al-Assadi had left the building about a half-hour earlier, al-Nedawi said. It was not clear if he was the target.

A neighbor was killed and four armed guards for the compound were wounded, al-Nedawi said. Following the blast, U.S. troops blocked roads leading to the offices.

Meanwhile, a roadside bomb targeting a U.S. Marine convoy in the Anbar provincial capital of Ramadi instead killed two civilians and wounded two others, said 1st Lt. Blanca Binstock, a spokeswoman. Ramadi is an insurgent stronghold 70 miles west of Baghdad.

Another roadside bomb missed a U.S. military convoy in the New Baghdad district but killed a civilian and wounded three others, police Capt. Mohammed Izz al-Deen said.

A police patrol struck a roadside bomb at a checkpoint on Baghdad's outskirts, wounding two policemen, 1st Lt. Mohammed al-Hayali said.

In western Iraq, U.S. Marines conducting raids aimed at disrupting foreign fighter networks defused nine roadside bombs Friday, a day after a light armored vehicle struck a mine, wounding six Marines, a company commander said.

A supply convoy entering the city of Hit found the roadside bombs spread along 500 yards of a major artery, and Marines participating in Operation Sword traced trigger wires to a school, said Maj. Steve Lawson, of Columbus, Ohio, commander of the 3rd Battalion, 25th Marine Regiment.

Marines finished searching houses for weapons Friday morning in 122-degree heat and began foot patrols in the city, about 85 miles west of Baghdad in volatile Anbar province. The operation began Tuesday with more than 1,000 U.S. troops and Iraqi soldiers.

Lawson said his company detained 10 suspected insurgents, and one of its tanks killed a man moments after they saw him trigger a roadside bomb.

The six Marines wounded Thursday suffered broken legs and concussions.

A fire at a power station that supplies a Baghdad waterworks shut down the facility, leaving millions of people without drinking water, officials said.

The blaze came a day after Baghdad's mayor decried the capital's crumbling infrastructure and the lack of clean water and threatened to resign if the Iraqi government did not provide more money.

The fire halted all distribution from the Karkh water station in Tarmiyah, which serves northern and western Baghdad, and repairs could take at least three days, said Jassim Mohammed, the project's director.

While Mohammed said he believed a bomb started the fire, a municipal official said the blaze was still under investigation.

While militants frequently target infrastructure, loud explosions can occur when a transformer blows.

Iraqi engineers told the U.S. military the fire resulted from a blown transformer and not an insurgent attack, said Sgt. 1st Class David Abrams, a spokesman for Task Force Baghdad.

"We verified with engineers on the site that it was a blown transformer," Abrams said.

Efforts to expand Baghdad's water supplies were set back in June when insurgents sabotaged a pipeline near Baghdad.

Mayor Alaa Mahmoud al-Timimi's threat to resign over the dismal state of the capital's infrastructure was an indication of the daily misery that Baghdad's 6.45 million people still endure more than two years after the U.S.-led invasion. They are wracked not only by unrelenting bombings and kidnappings but serious shortages of water, electricity and fuel.

"It's useless for any official to stay in office without the means to accomplish his job," al-Timimi said Thursday.

Al-Timimi wants $1.5 billion from the Iraqi national government for Baghdad in 2005 but so far has received only $85 million, said his spokesman, Ameer Ali Hasson.

Some complain their water smells bad, and Hasson acknowledged that in some areas, it gets mixed with sewage.

"The problem is escalating," said al-Timimi, a Shiite who took office in May 2004.

According to City Hall, Baghdad produces about 544 million gallons of water per day, some 370 million gallons short of its required amount. Some 55 percent of the water is lost through leakage in the pipes.

Elsewhere, an Iraqi national guard battalion found a huge ammunition stockpile, including hundreds of mortar shells and rockets, near Karbala, 50 miles south of Baghdad, according to video from Associated Press Television News.

The stockpile was buried in the desert south of Karbala, and Iraqi guardsmen believe it is part of ammunition insurgents frequently use against U.S. troops and Iraqi security forces.