A suicide bomber rammed a lorry packed with explosives into the United Nations headquarters in Baghdad yesterday, killing the UN special representative and as many as 19 others, including a British woman.

More than 100 people were injured in the blast, and four employees of the World Bank, which was using the UN offices as a base, and a consultant were reported missing.

The International Monetary Fund said some of its employees had also been caught up in the explosion.

Rescue workers spent hours digging with their hands though the rubble of the UN building in a desperate attempt to save the UN special envoy, Sergio Vieira de Mello. At first he was conscious and able to speak to his staff by phone. But the connection was lost and the Brazilian envoy died in the ruins of his office.

The explosion detonated below Mr Vieira de Mello’s room on the second floor and left the diplomat trapped with his legs beneath an iron bar.

His last words, spoken in a weak voice to colleagues from beneath the rubble, were “water, water”, witnesses said.

The British woman who died was named as Fiona Watson, 35, from Fife, who worked in Mr Vieira de Mello’s office on the Oil-for-Food programme.

Kofi Annan, the UN Secretary-General, said that everyone at the organisation was shocked and dismayed by the attack, which left scores injured, many of them drivers and security staff.

“Nothing can excuse this act of unprovoked and murderous violence against men and women who went to Iraq with one purpose only — to help the Iraqi people recover their independence and sovereignty,” he said. His under-secretary, Shashi Tharoor, told the BBC that the United Nations would have to review its presence in Iraq.

The bombing was the bloodiest since President Bush declared an end of hostilities in Iraq on May 1. It could have severe repercussions for the UN’s role in Iraq, where its agencies are leading relief efforts and helping to establish a post-Saddam government. A grim-faced President Bush interrupted his holiday in Texas to vow that America would fight back.

“We will persevere through every hardship,” he said. “The terrorists want to return to the days of torture chambers and mass graves.”

Tony Blair, on holiday in Barbados, said: “I am shocked and saddened by this news.

“The perpetrators of the atrocity have demonstrated pure cowardice and are enemies not only of the UN and the coalition but also of the Iraqi people.”

There were suspicions last night that the bombing was the work of the al-Qaeda network, or its local Iraq affiliate, Ansar al-Islam.

Both groups have been infiltrating fighters into Iraq over the past few weeks. They were also blamed for a similar bombing outside the Jordanian embassy in Baghdad this month that killed 17 people.

A senior coalition official warned The Times this week that the bombing of the embassy could mark the start of a new wave of attacks on “soft targets”, which are easier to hit than the military convoys and checkpoints that have been the main focus of recent attacks.

Fawzi Sarhan al-Hamdani, who was outside the UN building in mid-afternoon, said he saw a man drive a yellow cement mixer through a locked gate at the side of the compound before the blast shattered the windows of his car and gashed his arm.

The blast brought down a corner of the three-floor building, cascading tonnes of rubble on those trapped inside and spreading carnage in the car park outside, where Iraqi drivers and security guards were working.

Although protected by security guards, the building is regarded as a “soft-target”, compared with the heavily defended US military sites.

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