BAGHDAD, Aug 19: A massive truck bomb devastated the United Nations headquarters in Baghdad on Tuesday, killing the UN special envoy to Iraq and at least 16 others in what may have been a suicide attack, officials said.

Scores were wounded and rescue workers battled into the night to save those trapped in the rubble as US President George Bush vowed not to be intimidated by “terrorists” and diehard supporters of former Iraqi president Saddam Hussein.

Mr Sergio Vieira de Mello, UN Secretary General Kofi Annan’s new special representative to US-occupied Iraq, survived for several hours in the wreckage of his office. It took the full force of the blast and may have been targeted. Some of the UN’s 300 or so staffers were still trapped in the rubble, officials at the scene said.

But the 55-year-old Brazilian diplomat, who made a career defending human rights, died of his wounds, a UN spokesman said. He was a plain-speaking figure, respected round the world.

The US president halted a golf outing after hearing the news of the explosion and returned to his Texas ranch, where he gave an official statement. “These killers will not determine the future of Iraq,” Mr Bush said.

The UN complex houses a number of its agencies and was the base for inspectors during the hunt for Iraq’s alleged weapons of mass destruction.

Television pictures from inside the three-storey building showed a man addressing reporters when it went dark at the sound of a huge explosion around 4.30pm (5.30pm PST). It became a murky scene of dust and frightened people with bloodied faces.

The attackers may have been aiming as much to discredit the US occupying forces as to strike at the United Nations, whose main role in Iraq is providing humanitarian aid, analysts said.

Clouds of black smoke ruffled the sky blue UN flag in the hot Baghdad evening as dazed and bleeding workers were led from the rubble by US soldiers, some of them ferried off on stretchers to hospitals by military helicopters.

“I saw legs and arms, charred remains,” said journalist Grant Hodgson, who was at a UN news conference when the blast struck. The search for survivors continued as darkness fell.

Last week, the UN security council set aside bitter differences over the US invasion and set up a mission to coordinate its mainly humanitarian effort in Iraq. Washington has rejected transferring power to the United Nations, although it would like more countries to share the burden of running the country.

There was no claim of responsibility for the explosion, just as there was none two weeks ago when a truck-bomb shattered the Jordanian embassy in Baghdad, killing 17 people. US forces say militants or diehard supporters of Saddam Hussein might have set that bomb — on a “soft target” to weaken the US grip over Iraq.

“The explosion was caused by a massive truck bomb,” Bernard Kerik, the senior US police official in Baghdad, said. “We have evidence to suggest it could have been a suicide attack.”

“It’s people that don’t want us to succeed,” he said. “It’s the same people who are fighting the (US-led) Coalition.”

UN officials said it may have been a cement truck.

UN COUNCIL: Speaking before he confirmed the envoy’s death, chief UN spokesman Fred Eckhard stressed that the US occupying force was responsible for providing security in Iraq.