US Central Command had said that its aircraft fired on Iraqi rocket launchers in the area and that civilian casualties could not always be avoided. There was no categoric admission of responsibility, however, and the Pentagon claimed later that an Iraqi surface-to-air missile could have fallen back on the market.

“Coalition forces did not target a marketplace nor were any bombs or missiles dropped or fired in the district,” Major-General Stanley McChrystal said. “We don’t know for a fact whether it was US or Iraqi. We can’t make any assumption at this point. We’ll continue to look and see if we missed anything. But another explanation could be that triple-A (anti-aircraft artillery) or a surface-to-air missile that missed its target fell back into the marketplace area.”

Earlier, Brigadier-General Vincent Brooks at US Central Command also implied that the explosion might have been caused by the Iraqis, saying “what meets the eye isn’t always true”.

In a later statement, US Central Command then seemed to confirm that the market in Baghdad had been hit by coalition missiles. “The missiles and launchers were placed in a civilian residential area, most positioned less than 300ft from homes. A full assessment of the operation is ongoing. The missiles were a threat to coalition forces.”

More than 30 other people were injured in what would be the worst documented incident of civilian casualties since the aerial bombardment of the city began six days ago.

A pregnant woman was among the dead. Many of the victims had been reduced to charred bodies and were hard to identify among mangled cars and collapsed and blackened buildings.

Enraged Iraqis carried bloody bodies away, yelling slogans denouncing President Bush and pledging loyalty to the Iraqi President. “We will sacrifice our blood and souls for you, Saddam,” they chanted. “Down with Bush.”

Kofi Annan, the United Nations Secretary-General, gave a stern warning to coalition forces about the need to avoid civilian casualties. He said: “I must say I am getting increasingly concerned by humanitarian casualties in this conflict.

“I would want to remind all belligerents that they should respect international humanitarian law and take all necessary steps to protect civilians.”

Residents and Iraqi officials said that two missiles had hit the market at about 11.30am yesterday. Haneed Dulaimi, a civil defence official, said: “Two missiles hit the street.”

He said that there were no military facilities in the area of the Shaab district, which is made up of ground-floor shops and restaurants beneath apartment blocks. But some local people said there was a military compound near by.

The incident threatened to wreck the Pentagon’s carefully constructed war plan to avoid civilian targets while hitting the instruments and symbols of Saddam’s power. Inflaming anti-US opinion among Baghdad residents was just what Washington was trying to avoid ahead of a potentially bloody battle for the Iraqi capital.

In the wider Gulf region, pictures of the scene after the explosion were picked up by Arab-language satellite channels and threatened to deepen Muslim cynicism towards Washington’s insistence that US forces were fighting the war as liberators.

Donald Rumsfeld, the US Defence Secretary, has repeatedly said that the US bombardment of Baghdad is without precedent because of the precision with which the targets are being selected. Mr Bush, addressing military chiefs during a visit to US Central Command headquarters in Tampa, Florida, underlined the message, saying that the US was using “lethal precision” to hit vital military targets.

But Geoff Hoon, the British Defence Secretary, adopted a more realistic stance towards the risk of civilian casualties, saying: “As we move forward, those risks are increased and obviously, as the aerial campaign has demonstrated, there are risks to civilians.”

General Brooks said that “mistakes can occur”.

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