The latest round of bombing began at 7:35 p.m. local time, setting off a series of explosions and prompting anti-aircraft fire.

The four US soldiers were killed when a taxi driver blew up his vehicle at a checkpoint north of the city of Najaf, some 150 km from the capital, a US military spokesman told reporters.

Baghdad said the suicide bomber, an Iraqi Army officer, was seeking to teach the Americans a "lesson" and warned of more such attacks to come.

"This is only a beginning and you will hear good news in the coming days. We will use any means to stop the enemy and kill the enemy," Iraqi Vice President Taha Yassin Ramadan warned.

"The United States will turn the whole world into martyrs against it."

Thousands of Arab volunteers are flowing into the country to help Baghdad fight the war against the United States and Britain, Ramadan added.

Ramadan lambasted the US and British governments. "They are bragging that a B-52 bomber can... kill 500 people at a time... That's why people are transforming themselves into bombs," he said.

"One day, we will see that one martyr operation will kill 5,000 instead of the 500 you kill with your bombs."

A state television presenter, describing the attack as a "blessed beginning on the road of sacrifice and martyrdom", said President Saddam Hussein had awarded medals to the dead bomber, an army officer.

Iraqi television named the dead bomber as Ali Hammadi Al-Namani and said he had killed 11 Americans, not four.

The suicide attack, the first against US-led forces since they invaded Iraq on March 20, threatens to complicate Washington's task of defending long supply lines and preparing for a major battle for Baghdad.

US officers in the field said there would be a pause in the advance on Baghdad for four to six days to consolidate supply lines. Headquarters commanders said they would press on with the war on many fronts.

A US spokesman, Major General Victor Renuart, said earlier that the car bomb appeared to be a "terrorist" attack by an organization that was getting "a little bit desperate", adding that it would not affect military operations.

After the attack, Iraq's chief Muslim cleric issued a fatwa, or religious decree, calling on the people to wage holy war against the US and British forces.

However, a British military spokesman played down reports of a pause in the ground campaign, calling the reorganization of ground forces "purely a case of shaping the battlefield."

The United States says it was checking to see whether its forces were responsible for a devastating explosion in a crowded Baghdad market on Friday evening. A hospital doctor said the toll from the attack had risen to 62 dead and 49 wounded.

Shiites in the stricken Shula district voiced fury at the United States. Many were also angry that Iraqi missile launchers and anti-aircraft guns had been sited in their neighborhood.

In the overnight blitz on Baghdad, at least one cruise missile crashed into the roof of the Information Ministry, wrecking aerials and satellite dishes.

Elsewhere an allied air attack on a crack unit of Iraq's Republican Guards near the city of Karbala killed at least 55 Iraqi soldiers and destroyed more than 25 vehicles, US military officials said.

Two battalions of Apache helicopters from the 101st Airborne's Aviation Brigade struck 40 targets of the Republican Guards' Medina Division during the attack late Friday, Major Hugh Cate told reporters.

Coalition forces also destroyed a building which was hosting a meeting of some 200 members of Iraq's ruling Baath Party around the southern city of Basra, a US general said yesterday.

A defense official said troops from the Army's 82nd Airborne Division had been placed near Nassiriyah, 375 km (235 miles) southeast of Baghdad, to boost security for convoys.

In another reminder of the strong Iraqi resistance, the bodies of the first British servicemen to die in the war were flown home yesterday, as anti-war demonstrations were kicking off across the country.

Meanwhile Iraqi Kurdish rebels were consolidating their new positions outside the northern oil city of Kirkuk, with Iraqi government forces keeping up sporadic artillery and rocket fire.

The United Nations adopted a resolution allowing the resumption under sole UN authority of humanitarian aid for Iraq through its "oil-for-food" program, suspended at the start of the war.

But Iraq rejected the move, saying the program could not go forward without Baghdad's consent.