Staff in shock after explosion claims the life of the UN's own 'action man'

Sergio Vieira de Mello's last telephone call was to summon rescue workers to the wreckage of his office where he lay dying after yesterday's bomb blast.

It was clear from the moment of the blast that the top UN envoy in Iraq must be seriously hurt, because the bomb exploded right outside the window of his third floor office, destroying that section of the Canal Hotel where the UN headquarters are located.

News that one of the most respected figures in the UN system was critically injured shocked thousands of international staff, who watched the tragedy unfold live on television.

First reports had seemed hopeful the Brazilian-born diplomat would survive: trapped in the rubble of his office, he had the presence of mind to telephone Iraqi authorities for help, and they were later said to be mopping his brow with water. But as the afternoon wore on, the silence told its own story.

Mr Vieira de Mello was as close as the UN gets to having an action man. The 55-year-old fitness fanatic was never a stranger to danger. He came to international prominence in 1999 when he steered East Timor towards independence, as rampaging pro-Indonesian militias tried to block the process every step of the way. On his office wall was a poster asking visitors to unload their weapons.

His success during his three years as head of the UN administration in East Timor impressed the Americans, who were looking for an effective replacement for Mary Robinson as UN human rights commissioner.

Mr Vieira de Mello stepped into the breach in July last year, looking forward to four years as the world's top human rights advocate. He was already being tipped as a possible successor to Kofi Annan, when the Ghanaian's second term expires.

But then the Americans came calling again, looking for a UN official who could navigate the troubled diplomatic waters of post-Saddam Iraq amid the bitter recriminations among the major powers on the Security Council. Mr Vieira de Mello fitted the bill, having learnt how to work the system during his 34-year UN career in which he rose to become the under-secretary general for humanitarian affairs in New York.

He agreed to pick up the poisoned chalice and headed for Iraq in June as UN representative. But first, he insisted on a four-month assignment so that he could return to his duties as high commissioner for human rights in Geneva.

Once in Baghdad, Mr Vieira de Mello pulled no punches within the murky terms of his mandate in which the US and British occupiers agreed only to give the UN a "co-ordinating" role. Admitting that he was in a "bizarre situation", he decided to make the best of a bad job, insisting that his top priority was "to make sure that the interests of the Iraqi people come first" as they began to rebuild their country.

He played a discreet but vital role in assisting the Americans in putting together the new executive body to emerge in Iraq after the fall of President Saddam Hussein - the provisional Governing Council.

Mr Vieira de Mello was mandated to work with the British and the Americans to co-ordinate humanitarian and reconstruction assistance, assist refugee returns, promote human rights and "facilitate a process leading to an internationally recognised representative government of Iraq". By the time of his death, he was coordinating the work of hundreds of UN humanitarian staff, including 30 or 40 people who worked in his office.

A close associate, Ahmad Fawzi, who was still in a state of shock as he watched the television images of yesterday's carnage while on holiday in London, described the polyglot Mr Vieira de Mello as "one of the stars of the UN system".

The diplomat had known that he would be in danger in Iraq but that had never stopped him before: his previous humanitarian and peace-keeping assignments had included a stint running the UN mission in Kosovo, demining in Cambodia and co-ordinating relief to the troubled Great Lakes region of central Africa.

It was only last month that Mr Vieira de Mello told the Security Council, in what now seems eerily prescient: "The UN presence in Iraq remains vulnerable to any who would seek to target our organisation."

Brazil declared three days of mourning last night for the UN envoy. Amnesty International, which had championed Mr Vieira de Mello's appointment, paid tribute, saying his contribution to human rights "will never be forgotten".