BAGHDAD, Iraq -

Gunmen ambushed a convoy carrying Shiite Muslim pilgrims home from Saudi Arabia on Wednesday in central Iraq, killing 11 people, a provincial governor said, the latest example of the violence U.S. President George W. Bush hopes to quell by announcing a new strategy for the country.

U.S. and Iraqi forces, meanwhile, chased militants in and out of alleys and conducted house-to-house searches in a central Baghdad neighbourhood, a day after fierce fighting that killed 50 insurgents.

An Iraqi army officer said 15 suspects had been arrested in Baghdad's troubled Haifa Street section. He spoke on condition of anonymity because of security concerns.

The attack on the pilgrims returning from the hajj occurred 120 kilometres west of the Shiite holy city of Karbala, just inside the Sunni insurgent stronghold of Anbar province. Thousands of Iraqis returning from the annual pilgrimage to Saudi Arabia have been using the highway leading to southern Iraq that passes through Anbar.

Gunmen opened fire on buses carrying 120 Shiites returning from Saudi Arabia to the central province of Babylon, killing at least 11 and wounding 14, Karbala provincial Gov. Akeel al-Khazaali said. Karbala police spokesman Rahman Mishawi confirmed the attack and said many of the injuries were serious.

The attack came a day after some Sunni politicians and clerics said a number of pilgrims were kidnapped by Shiite militiamen wearing Iraqi security uniforms shortly after passing through the Arar border crossing point between Saudi Arabia and Iraq. Prime Minister Nouri al-Maliki's office denied the claim.

Sunni insurgents and Shiite militiamen have been targeting followers of their rival sects in the past months, leaving thousands of people dead.

At least 92 violent deaths were reported by police in Iraq, including 67 bullet-riddled bodies that were found, most in Baghdad. The U.S. military also said three American soldiers were killed Tuesday in fighting.

On Wednesday, a suicide bomber walked into a crowd of people milling outside a police station in the northern city of Tal Afar, killing four civilians and wounding a dozen, police said. Another bomber targeted the convoy of the Tal Afar mayor, killing a child, police said. The mayor was unharmed.

Bush is expected to announce that he will send 20,000 more soldiers to Iraq as he seeks to win support for the unpopular war, despite growing opposition in Congress.

Defence Minister Abdul-Qader al-Obaidi also revealed new details of a new security plan announced by al-Maliki days earlier, saying it had three or four phases and "the first stage has already begun.''

Al-Obaidi did not elaborate on what steps the government had taken or say whether the Haifa Street operation was part of the security plan. He said that offensive was launched in response to the killings of 27 people there on Saturday.

"This is what made us decide to go into Haifa street,'' al-Obaidi told The Associated Press. He added that at least seven foreign Arabs were captured, including some who entered Iraq recently.

An Iraqi army general, speaking on condition of anonymity because of the sensitivity of the plan, said the Haifa Street battle was not part of the new Baghdad security plan.

U.S. and Iraqi forces spent the day in a mopping up operation in the dangerous neighbourhood, trying to ensure that insurgent forces were cleared from the area.

U.S. tanks lined the streets in the neighbourhood, a militant Sunni Arab stronghold just north of the heavily fortified Green Zone _ home to the U.S. Embassy and other facilities.

Haifa Street is a broad, two-lane thoroughfare that stretches northwest from the Green Zone through the heart of Baghdad along the Tigris River. It was once a well-to-do enclave under Saddam Hussein and many prominent Baathists made their homes there. It has since fallen into disrepair, and discount shops have replaced upscale boutiques. Some storefronts are shuttered altogether.

Al-Maliki aides have said the security operation would target Sunni insurgents first, rather than Shiite Muslim militiamen blamed in sectarian killings. U.S. officials have said the additional U.S. troops deployed under Bush's new strategy would work with Iraqi troops to put down both Sunni insurgents and Shiite militiamen.

In an interview published Wednesday, Sunni leader Harith al-Dhari -- head of the influential Association of Muslim Scholars, a group with ties to some Sunni insurgents -- said the offensive would not provide balanced security.

"This government has taken as its job to slaughter, arrest, abduct and displace (Sunnis). It is not taking its responsibility for a real security or economy or even providing services for the Iraqi people,'' al-Dhari was quoted by the Saudi newspaper Al-Watan as saying.

Elsewhere, Iraqi National Security Adviser Mouwaffak al-Rubaie said the country's top Shiite Muslim cleric agreed that illegal weapons should be removed from the public, an indication that the spiritual leader will support the U.S. security plan.

Al-Rubaie said he briefed Grand Ayatollah Ali al-Sistani on the plan in the holy city of Najaf, but he did not release any details.

Al-Sistani's support would be an important boost for the security plan. The Iranian-born cleric's word is considered law by many Shiites, but his failure to rein in suspected Shiite death squads has raised questions about the extent of his influence.

President Jalal Talabani also said the government should delay the execution of Saddam Hussein's half brother and former intelligence chief, Barzan Ibrahim, and Awad Hamed al-Bandar, former head of Iraq's Revolutionary Court.