Iraq's daily barrage of attacks took the lives of two more American soldiers and an employee of a UN-affiliated relief agency yesterday.

It came as thousands of followers of a hardline Shiite Muslim cleric marched on a US headquarters in the holy city of Najaf, demanding US forces leave the town and shouting slogans against the newly-formed Iraqi Governing Council.

The two American soldiers died when their convoy was struck by rocket-propelled grenades and small arms fire near Tal Afar, a town west of the northern city of Mosul, said a US military spokesman. Another American soldier was injured. All of the victims were from the 101st Airborne Division.

The deaths brought to 151 the number of American soldiers killed in action since the March 20 start of the war, four more than the total killed in the 1991 Gulf war.

Also yesterday a US soldier was killed and two others injured when their vehicle crashed and flipped over near Baghdad International Airport, according to a statement from US Central Command in Tampa, Florida.

The area of the convoy attack near Tal Afar had been relatively peaceful in recent weeks, and the ambush was a worrying development for forces trying to bring stability to Iraq.

Most of the recent violence has occurred in an area north and west of Baghdad called the Sunni triangle, where some support for Saddam Hussein remains.

In another troubling sign, a two-car convoy carrying members of the International Organisation for Migration was ambushed on a road near the southern city of Hilla when a pick-up truck pulled up alongside one of the vehicles and opened fire.

One person, an Iraqi driver, died after the car collided with a bus. Three other people were wounded, including one staff member who suffered a broken arm and ankle.

Omer Mekki, the deputy director of the World Health Organisation in Iraq, said personnel in the WHO convoy travelling minutes behind the IOM vehicles treated the injured and took the driver to hospital, where he died. Both convoys were clearly marked as United Nations vehicles.

"We're a bit shaken. Everybody is a bit shocked," said Mekki. "But when we were recruited and we came to Iraq, we knew there were risks. An incident like this is not unexpected."

Ahmed Fawzi, a spokesman for the special representative of UN Secretary-General Kofi Annan, denounced the attack. "The United Nations is in Iraq to help the Iraqi people.

"We are not taking sides. We are neutral," he said in Baghdad.

"We have no way of knowing whether this was targeted at the United Nations. This is a dangerous situation. Only the restoration of law and order can put an end to these attacks," he said.