Security at the UN compound in Baghdad was stepped up before a devastating bomb blast there earlier this week, a senior UN health official said Friday as he gave a harrowing account of his narrow escape from the atrocity which killed at least 23 people.

"We were on a much higher level of security protection than usual," said David Nabarro, of the World Health Organisation (WHO), who is helping to plan the rehabilitation of Iraq's health services.

Nabarro attended a meeting in the UN building in Baghdad next to the epicentre of the blast and was wounded by shards of glass in the back of his neck.

A trained medical doctor, he explained in graphic detail how he and his colleagues clambered out of the wreckage of the building and tried to bring medical help to people with massive wounds caused by the truck bomb.

"We were in a cloud on our own in this fog of moaning and crying," he said after returning from Baghdad.

"It was like an earthquake."

Nabarro told journalists here that there had been a heightened sense of security "for about the last week or two".

"When you come in through the front entrance they were very meticulous on security, searching underneath the vehicle," he said.

"In fact they'd stepped up security because there was bit of a worry of something big perhaps happening, but not necessarily to the UN," he added.

At least 23 people were killed, including senior UN envoy Sergio Vieira de Mello, and more than 100 wounded in the suicide bomb attack on Tuesday, which destroyed part of the UN base in the Iraqi capital, the Canal Hotel.

A shocked Brazil mourned the death on Tuesday of Sergio Vieira de Mello, the UN envoy in Iraq, hailing him as a man who brought honor to his country through his work for peace in world conflict zones.

Vieira de Mello, 55, a native of Rio de Janeiro, was killed when a truck bomb wrecked the UN headquarters in Baghdad.

He was trapped in the rubble for several hours before succumbing to his wounds and Brazilians watched as the tragedy unfolded on TV.

"Oh my God, oh my God," said Foreign Minister Celso Amorim as he received the news by telephone.

President Luiz Inacio Lula da Silva called for a minute of silence during his meeting with Chilean President Ricardo Lagos.

Lula da Silva declared three days of mourning for the late envoy, known for his immense charm as well as his skilful diplomacy.

He was a victim of "terrorist insanity", Lula da Silva said.

Diplomats said the late envoy was a front-runner to succeed Kofi Annan as UN secretary-general.

Vieira de Mello attended university in Paris before a 33-year UN career that took him from Lebanon to Africa, Cambodia to East Timor, and to Iraq.

Though he made his home outside Brazil, Brazilians were immensely proud of him. Former President Jose Sarney called him "one of the best Brazilian men" .

Paulo Delgado, the ruling Workers Party foreign affairs chief, also praised him, especially for his stance toward the United States.

"He took a firm position with the US, demanding that they re-establish water and electricity. He said deploying tanks in Iraq was like rolling tanks into Copacabana [Rio's beachfront area]." FLOWN HOME

A Brazilian air force jet carrying the body of UN envoy to Iraq Sergio Vieira de Mello took off from Baghdad airport Friday bound for Geneva.

In a ceremony to mark the repatriation of the body, De Mello's coffin, draped in a UN flag, was loaded onto the back of the jet by six pall-bearers, including his bodyguards, accompanied by two pipers playing Amazing Grace.

Moments later the grey plane rolled down the runway and took off.

Mourners, including the US civil administrator for Iraq Paul Bremer and members of the US-appointed transitional Governing Council, had earlier paid their last respects to the diplomat, who was killed in the suicide bombing of the UN headquarters here.

UN dignitaries, including Romero Lopes da Silva, the world body's head of humanitarian operations in the war-torn country, were also there.

"I am delighted that the UN has decided to stay here and they are going to open tomorrow," Bremer told the reporters after the ceremony.

"We will not be deterred by any act of terrorism. The rebuilding of Iraq by Iraqi people will go on. It's not going to be stopped by this act or any such act.

"It is a good lesson for the terrorists that they will open tomorrow," he said.

After the ceremony, a teary-eyed Bremer was seen consoling a weeping female UN worker.

The UN's oil-for-food programme director, Benon Sevan, had earlier hailed De Mello as a man who believed passionately in the work of the United Nations right to the end.

"Even under the most extreme pain, pinned down under rubble in his office, he said to First Sergeant Von Zehle Jr. of the coalition forces trying to rescue him, 'don't let them pull the mission out'."

Sevan added: "Bowing before you at this very difficult hour, I assure you that no heinous act of terrorism will deter us from carrying out the noble task entrusted to us in the service of the UN.

"We will overcome – we will stay the course."

During a brief stopover in Geneva, a UN official said there, De Mello's wife and two children will board the plane to accompany the body back to Brazil where it is to be received in a formal ceremony.

De Mello was one of at least 23 people killed in Tuesday's suicide bombing on the United Nations' offices in Baghdad, which also wounded more than 100.