The shooting occurred late Monday at a checkpoint manned by the US Army's Third Infantry Division at Najaf, 150 kilometers (95 miles) south of Baghdad, and came as civilian casualties continued to mount in the Iraqi capital.

"Civilians must be spared as far as is possible. Equally soldiers have the right to assure their own security and a balance between these two elements must be found," said Antonella Notarim, spokeswoman for the International Committee of the Red Cross (ICRC).

"I cannot make any comment on what happpened. We were not witnesses. I can only regret profoundly that once again civilians are affected," she added.

US military officials said US troops opened fire on the vehicle after it ignored two warnings to stop.

US forces in Iraq have been on a heightened state of alert and are approaching Iraqi civilians with caution following a suicide car bombing near Najaf on Saturday that killed four soldiers.

But in Brussels the European Commission appealed to combattants to "show their restraint when it comes to civilians."

"This is a horrible and tragic incident ... It is not an isolated incident. Too many civilians have already lost their lives in this war.

"It shows that however advanced the technology, there is no war without loss of innocent lives," said a spokesman.

The UN special rapporteur for human rights in Iraq, Andreas Mavrommatis also sharply criticised coalition bombardments which have hit Iraqi civilians.

"Respect to the right to life, to my mind, enjoins combatants to abort the process when the targeting of assets entails foreseeable risks to civilians," he told a press conference in Geneva.

"What we expect now is for the war to be over the soonest and that events such as the carnage in the market place in Baghdad would not occur again," Mavrommatis said.

The US media meanwhile warned of the accidental killing of civilians would have a sharp impact on public opinion in Iraq and the Middle East.

"Even if accidental, such events, like the deaths of civilians in Baghdad attributed to errant US bombs, can incur large political costs both in and outside Iraq," the Washington Post said.

The New York Times concurred, stating that, "... billions around the globe are seeing and hearing reports that women and children were gunned down yesterday while riding in a civilian van at an American checkpoint.

"This is just what the Iraqi commanders have in mind when they send soldiers disguised as noncombatants to fire on unsuspecting American troops. The killing of the soldiers is an incidental benefit.

"The real goal is to turn the Americans against Iraqi civilians and cause them to behave like a hostile occupying army rather than the friendly liberators we had envisioned," the paper said.

At US military headquarters in the Gulf state of Qatar, a senior US commander said civilian losses were regrettable but unavoidable in war.

"Our efforts may result in the loss of civilian lives and they clearly will result in the loss of Iraqi military lives," Brigadier General Vincent Brooks told a press briefing.

"While we regret the loss of civilian lives ... they remain unavoidable as they have been throughout history," he said.

SPACE.WIRE