Mr El Baradei beat both Bob Geldof and Bono, the U2 singer, who many expected would be rewarded for their work on Live 8 and third world debt relief, to claim the world's most prestigious humanitarian award.

As director of the IAEA, which is charged with preventing nuclear proliferation, Mr El Baradei had repeatedly clashed with Britain and the United States over the invasion of Iraq and the treatment of Iran and North Korea.

However, the Nobel Committee used the 60th anniversary of the bombing of Hiroshima and Nagasaki to highlight the peril of nuclear weapons and to further encourage steps towards their abolition. The award was praised by Japanese survivors from both bombed cities.

The committee's statement read: "At a time when disarmament efforts appear deadlocked, when there is a danger that nuclear arms will spread both to states and to terrorist groups, and when nuclear power again appears to be playing an increasingly significant role, IAEA's work is of incalculable importance."

Mr El Baradei yesterday said the $1.3 million Nobel award would give him and his agency a much needed "shot in the arm" as they tackle the nuclear crises in Iran and North Korea.

The Egyptian diplomat said he had been sure he would not win because he had not received the traditional advance telephone call from the Committee. He learnt of his win at home while watching television with his wife, Aida. He said he jumped to his feet then hugged and kissed her in celebration.

Mr El Baradei said: "The award sends a very strong message: 'Keep doing what you are doing - be impartial, act with integrity', and that is what we intend to do."

The Egyptian diplomat came to prominence before the US-led invasion of Iraq in 2003 by challenging Washington's stance that Iraq had weapons of mass destruction. No weapons were found after the overthrow of Saddam Hussein, while a programme discovered in the early 1990s appeared to have been abandoned as Iraq had claimed.

The US had opposed Mr El Baradei's reappointment to the post which he has held since 1997. Yet despite previous criticism, the US secretary of state, Condoleezza Rice, phoned to congratulate him yesterday.

Tony Blair, the Prime Minister, also praised the head of the IAEA. He said: "It is well deserved and very important and shows the significance that is attached to the work that agency does."

Kofi Annan, the UN secretary-general, the 2001 peace laureate, said it should be a wake-up call on the perils of nuclear war. He said that, at last month's UN summit: "We couldn't even agree on a paragraph on non-proliferation or disarmament. It was a disgrace. I hope that this award will wake us all up."

However, awarding the prize to Mr El Baradei has angered Greenpeace, the environmental group who yesterday said they was "shocked" at the decision and insisted that the UN agency's promotion of atomic energy had increased the risk of nuclear weapons proliferation.

Stein Toennesson, director of the Peace Research Institute-Oslo, said the award was surprising given that the IAEA remains bogged down by the standoff with Iran and that North Korea has now said it possesses nuclear weapons.

He said: "The prize was given to someone who did not have success during the year. We have to see the prize as, implicitly, an expression of hope that the Iran question can be solved within the IAEA."

The prize, named after Sweden's Alfred Nobel, a philanthropist and inventor of dynamite, was first awarded in 1901 and is due to be handed out in Oslo on Dec. 10.

Concerns remain over IAEA's dual missions|

THE Nobel Peace Prize, founded on a fortune made from explosives, has gone to the agency whose job it is to promote nuclear power without also promoting nuclear weapons. That probably deserves some kind of prize - but not a peace prize.

Mohammed ElBaradei and the IAEA have the task of policing the spread of nuclear weapons, but at the same time their declared job is to promote the very technologies and materials used to make those terrifying weapons. It's a job worthy of Dr Jekyll and Mr Hyde.

Opposing the Iraq war and championing a nuclear-free Middle East, Mr ElBaradei has in recent years been a voice of sanity in the world of nuclear non-proliferation.

But the Mr Hyde side of his job is to be the UN's frontman for the nuclear industry, peddling more nuclear power to more countries. And that is the part of Mr ElBaradei's job that worries us.

Greenpeace is concerned the horrors of Hiroshima and Nagasaki have begun to fade. We worry about nuclear materials falling into the hands of terrorists.

We worry about nuclear materials in nuclear power plants, reprocessing plants and storage facilities, because as long as these exist - materials pushed on states by the IAEA - there is no guarantee against the disastrous consequences of their theft or sabotage for use as weapons.

• Blake Lee-Harwood is campaigns director for Greenpeace

BLAKE LEE-HARWOOD