And this is from the UN's Daily Briefing website:

SECRETARY-GENERAL MOURNS SERGIO VIEIRA DE MELLO

The Secretary-General said in a statement, "The loss of Sergio Vieira de Mello is a bitter blow for the United Nations, and for me personally."

"The death of any colleague is hard to bear, but I can think of no one we could less afford to spare, or who would be more acutely missed throughout the UN system, than Sergio," he said. "Throughout his career he has been an outstanding servant of humanity, dedicated to relieving the suffering of his fellow men and women, helping them to resolve their conflicts and rebuild their war-torn societies.

"In his work with the peoples of every continent – as an official of the High Commissioner for Refugees, as Emergency Relief Coordinator, as my Special Representative in Kosovo and East Timor, and (all too briefly) as High Commissioner for Human Rights – in all those positions he impressed everyone with his charm, his energy, and his ability to get things done – not by force but by diplomacy and persuasion."

The Secretary-General went on, "In Iraq, where he spent the last months of his life, he was working day and night to help the Iraqi people regain control of their own destiny and build a future of peace, justice and full independence. It is tragic that he has now given his life in that cause, along with others who, like him, were devoted and much-loved servants of the United Nations. Those who killed him have committed a crime, not only against the United Nations but against Iraq itself."

He concluded, "I share the grief of Sergio's family. We shall all miss him sorely, as a colleague and as a friend. Let us also strive to be worthy of him, and to complete the work that he began, so that his death will not have been in vain."

Asked about Sergio Vieira de Mello, the Spokesman noted his long list of successes at the United Nations, saying that he had "distinguished himself as an active, capable doer." Of the attack, the Spokesman said, "Anything as dramatic as this is a setback."

He said it was too soon to think about a successor to Vieira de Mello, although the Secretary-General had been thinking of a replacement once his four-month term as Special Representative was set to expire.

Asked about other senior officials who had died in UN history, he noted the assassination of Count Folke Bernadotte in the late 1940s.