The American military also killed around 13 "terrorists" south of Baghdad, while three Iraqis, including a tribal sheikh and a mosque imam were murdered by gunmen in separate incidents.

Gunmen attacked a Shia wedding party and killed three relatives of the bridegroom south of Baghdad, security and medical sources said Friday.

The attack took place at 9:00 pm (1800 GMT) Thursday in Al-Wahda district, 30 kilometres (18 miles) south of Baghdad, near the town of Kut.

Police in Baghdad found 56 bodies and a severed head over the past 24 hours in various parts of the capital, the highest daily figure since the end of Ramadan, an Interior Ministry source said on Friday.

While not unprecedented, the number represents a sharp rise since last week when US forces were out in force throughout the city hunting for a missing US soldier.

Three US soldiers were killed in a single attack on Thursday afternoon when their vehicle hit a roadside bomb in Baghdad, the war-torn capital where 15,000 US personnel are battling to contain a vicious sectarian conflict.

On the same day, a marine was killed in Anbar province in the west of the country, the heartland of the al-Qaeda militant group in Iraq, a US statement said, while confirming another death "due to non-combat causes" on Wednesday.

The deaths brought to 2,822 the number of US troops to have died in Iraq since the March 2003 US invasion, and the mounting toll gives more ammunition to critics of President George W Bush's strategy.

Daily Iraqi civilian casualties from the war have fallen by about a fifth since the end of the Islamic holy month of Ramadan, but they still far outstrip US dead and Prime Minister Nuri al-Maliki's government remains fragile.

Baghdad seemed quiet on Friday morning as the bitterly divided Sunni and Shia communities prepared to head to their separate mosques to mark the weekly Muslim day of prayers under a total vehicle curfew.

But reports of unrest filtered in from other parts of the country.

US forces backed by air support approached two buildings near Mahmudiyah, a short distance south of Baghdad, where the suspected al-Qaeda militants were hiding. They called on those inside to surrender, the military said.

When the suspects refused to do so, the US troops entered the building and found five armed suspects, one of them in a explosive vest. "Coalition forces engaged and killed these five terrorists," a military statement said.

Then, approximately eight more suspects attempted to flee the scene and were shot dead by air and ground forces, it said, adding the assault was aimed at capturing an al-Qaeda operative.

Meanwhile, Sheikh Nahab Omran from the Shia Bani Hassan tribe in the Kafal district near the southern town of Hilla was killed by gunmen, police said.

Jassim Mohammed Ahmed, imam of the northern city of Kirkuk's biggest Sunni mosque was killed by gunmen in the city's Gharnata neighbourhood.

A fuel station employee was also killed west of Kirkuk by gunmen.

Civilian deaths run at around 100 per day, according to the latest UN figures, although the Iraqi government now refuses to release up-to-date tolls.

Against such a backdrop, and with unexplained gunfire heard late into the night in central Baghdad on Thursday, Bush's Republican party is facing a tough poll challenge from its Democratic opposition in Tuesday's vote.

The Democrats need to win 15 seats to capture the 435-seat House of Representatives and six seats to take the 100-seat Senate.

If they do so, Bush faces the prospect of finishing the last two years of his mandate as a lame duck president, hobbled by congressional inquiries into the conduct of the war and legislative obstruction.

A New York Times/CBS poll released Thursday showed only 29 percent of US voters approve of the way Bush is managing the war, equalling his lowest ratings from six months ago.

Bush has tried to counter Democratic charges that he has lost control of the conflict with an eleventh-hour campaign tour to bolster core Republican support and reverse opinion polls that show his party losing.

"The Democrats have no plan for victory, they have no idea how to win," Bush told supporters in Montana. "Harsh criticism is not a plan for victory. You can't win the war unless you're willing to fight the war."

The current US plan for Iraq is to support Maliki's coalition and build up Iraq's beleaguered security forces so that, within 12 to 18 months, they are ready to fight the insurgency without US military support.

This strategy has been knocked sideways, however, by the eruption of a sectarian war between Sunnis and Shias in parallel to the rebellion, and by shortcomings in the US-led reconstruction effort.

Iraqi President Jalal Talabani said on Thursday he did not envisage US-led forces withdrawing from his country before two to three years, despite Maliki's call for them to be ready to hand over to Iraqi forces within six months.