One of the four car bombs ripped through a crowded market in the southern town of Hilla killing at least 12 people and wounding 47 yesterday, police and health officials said.

In the mainly Shia town of Balad, north of Baghdad, the death toll from three huge car bombs on Thursday rose to 98 on Friday, hospital director Kassim Aboud said.

Furious residents in Balad blamed the attacks on "foreign fighters," long accused by the US military of infiltrating Iraq from Syria to carry out attacks across the country.

"What have those Jordanians and Palestinians and Saudis got to do with us? Shame on them!" Abu Waleed, a hotel owner in Balad who said seven people staying in his hotel died in the blasts, shouted angrily.

"Why is this happening? This is a criminal act and the constitution is going to succeed in spite of them," he cried.

Outside a hospital a doctor, Dawoud Allam, posted lists of the dead and the 119 wounded on a wall. Of the dead, 25 were children under 15, while 14 could not be identified, he said.

Crowds voiced their defiance by chanting: "With our souls, with our blood, we sacrifice ourselves for the constitution."

Insurgents are waging a campaign of suicide bombings, shootings and assassinations to try to topple Iraq's US-backed government. The constitution vote has raised sectarian tension between Iraq's Shia majority and the Sunni Arab minority.

Five US soldiers were also killed in one of the deadliest bombings on US forces in weeks, near Ramadi, a bastion of the insurgency west of Baghdad, the US army said on Thursday.

In Washington, the US commander in Iraq told senators plans to cut troop numbers next year might be thwarted if violence continued through the referendum and an election due in December. The number of Iraqi troops able to operate without US support had fallen to one battalion, he added.

The government, dominated by Shias and Kurds, has faced intensified attacks by the Sunni-led insurgency since elections in January.

Minority Sunnis have dominated Iraq for decades but have lost most of their influence since Saddam Hussein, a Sunni, was ousted in 2003. They fear that if the constitution is approved their marginalisation will be sealed.

The leader of al-Qaeda in Iraq, Abu Musab al-Zarqawi, has claimed responsibility for the wave of bombings.

With the latest US deaths, the total number of US troops to have died in Iraq since the US-led invasion of March 2003 rose to at least 1,929, with more than 13,000 wounded.

The United States has 149,000 troops in Iraq, with about 20,000 from other countries, nearly half of them from Britain.

Pentagon planners have said they hope to begin withdrawing US troops once Iraqi security forces, numbering about 190,000, are strong enough to handle the insurgency by themselves.

But the number able to operate without US forces has actually shrunk since July, US generals told US senators.

Just one of the 120 US-trained Iraqi army and police battalions could operate independently, General George Casey, the top US commander in Iraq, and General John Abizaid, top commander in the Middle East, said.

The Pentagon said in July the number was three.

"We fully recognize that Iraqi armed forces will not have an independent capability for some time because they don't have the institutional base to support them," Casey said.

Casey had said earlier this year he hoped for a substantial reduction in the number of US troops next year, but he said on Thursday that if things did not go well over the coming two and a half months, troops would have to stay.