BAGHDAD, Iraq — A representative of Iraq's leading cleric, the Grand Ayatollah Ali al-Sistani, was assassinated near the capital yesterday, in a development that further unsettled the strife-torn country as it prepares for elections.

Also yesterday, two U.S. Marines and a soldier were killed in action, and gunmen kidnapped a Turk from his hotel and killed at least six Iraqi Kurds in his employ.

The killing of his aide pointed to al-Sistani's central role in the struggle in which a Sunni-dominated insurgency has waged a campaign of bombings, assassinations and other acts of intimidation to disrupt Iraq's election.

Sheik Mahmoud Madaini, al-Sistani's representative in the town of Salman Pak, about 10 miles southeast of Baghdad, was gunned down as he returned home from a local mosque shortly after presiding over evening prayers. Madaini's son and four bodyguards also were killed.

Al-Sistani, arguably the most powerful figure in post-Saddam Hussein Iraq, is the senior Shiite cleric in a country where Shiites make up about 60 percent of the population. The favorite to win the most seats in the 275-seat transitional assembly in the Jan. 30 election is a slate of mainly Shiite candidates known as the United Iraqi Alliance, but usually referred to as "al-Sistani's list" because he is thought to favor it.

The cleric is not a candidate, although he has vigorously supported the election and resisted calls for its postponement.

While there is a history of violence among Shiite groups, recent attacks against al-Sistani's associates are widely believed to be the work of Sunni insurgents.

Insurgent groups, which U.S. officials say are made up mostly of disaffected Sunnis and former elements of Saddam Hussein's regime, have targeted government officials, electoral workers, police and soldiers in their campaign to topple the interim government appointed by the U.S.-led military coalition. They have also killed Shiite clerics and thousands of Shiite civilians.

Sheik Hussein Harithi, an al-Sistani representative in Baghdad, was assassinated five months ago in a neighborhood west of the capital after participating in a forum on the elections.

There have been several attempts to kill Sheik Abdul-Mehdi Kerbalai, al-Sistani's representative in the Shiite holy city of Karbala.

Despite his power, al-Sistani has opted not to take political office or play a visible role in the political jostling to fill the power vacuum left by Saddam's ouster. Unlike Iran's powerful ayatollahs, al-Sistani does not advocate an Islamic theocracy, believing instead that clerics should involve themselves more with social than political issues.

He possesses an ability to marshal thousands — peaceful protests have given him virtual veto power over U.S. electoral planning — and has rankled U.S. officials by refusing to meet directly with them. He displayed this power last year to almost single-handedly scuttle the original election formula proposed by former Coalition Provisional Authority administrator L. Paul Bremer that called for a complicated series of regional caucuses to select a national Parliament.

With U.N. envoy Lakhdar Brahimi as go-between, U.S. officials settled on a compromise acceptable to the cleric: a six-month delay in exchange for direct elections by the end of January.

Last summer, al-Sistani brokered a dramatic peace agreement that ended a weeks-long siege of the Imam Ali shrine in Najaf by supporters of militant cleric Muqtada al-Sadr. Late last year, calls for a postponement of the vote largely died in the face of al-Sistani's opposition.

Al-Sistani's role as unofficial godfather of the Shiite powerhouse United Iraqi Alliance has been a source of controversy.

The use of his picture to promote Alliance candidates has prompted growing complaints from other parties. Sharif Ali bin Hussein, head of the Constitutional Monarchy Party, has lodged a complaint over what he considers a violation of the campaign ban on religious symbols.

Adil Lami, a member of the Iraqi Electoral Commission, said commission rules ban the use of religious symbols such as crosses or pictures of the Quran in campaign material. The use of al-Sistani's image would constitute a violation, but Lami said he wasn't aware of any such cases.

On Tuesday, the Iraqi List slate led by interim Prime Minister Ayad Allawi issued a statement protesting the use of al-Sistani's image in Alliance materials, pointing out that the cleric is "not nominated on or supporting this list" or any other specific slate.

The violence that has marked the run-up to the elections continued yesterday.

A U.S. military statement said two Marines, assigned to the 1st Marine Expeditionary Force, were killed "while conducting security and stability operations in the al-Anbar Province."

A U.S. soldier died near Mosul, the U.S. military said today.

As of yesterday, at least 1,359 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The killing of the Kurds and seizing of the Turk occurred at the Bakhan Hotel in central Baghdad. Ten armed men emerged from two cars and opened fire on a minibus that was picking up the Turk.

There were conflicting reports about whether the kidnapped Turk, who had been in Iraq for about a year, is a businessman or construction worker.

Nearly 180 foreigners have been taken hostage in Iraq since last April; more than 30 of them have been killed. A French journalist was kidnapped last week.

Also yesterday, U.S. troops clashed with insurgents in Baghdad's northern Azamiyah neighborhood, The Associated Press reported. Some Iraqis were killed, witnesses said, and several cars were scorched by fire.

In the city of Baqouba, northeast of Baghdad, gunmen killed a member of Diyala province's governing council.

Additional information from The Washington Post, Reuters, the Chicago Tribune and The Associated Press.