Oslo (AFP) - Nuclear disarmament campaign group ICAN won the Nobel Peace Prize on Friday for its efforts to consign the atomic bomb to history, firing off a warning that Donald Trump's presidency showed the true extent of the risk posed by weapons of mass destruction.

More than 70 years since atomic bombs were used on the Japanese cities of Hiroshima and Nagasaki, the Nobel committee praised ICAN's non-proliferation efforts as nuclear-related crises swirl around North Korea and Iran.

The decision sent a clear message at a time when Trump has threatened to tear up a 2015 deal curbing Iran's nuclear abilities. And the US president alarmed delegates at the UN General Assembly last month by warning he might be forced to "totally destroy" North Korea because of its atomic weapons programme.

"We live in a world where the risk of nuclear weapons being used is greater than it has been for a long time," Norwegian Nobel committee president Berit Reiss-Andersen said in announcing the prize in Oslo.

Founded in Vienna in 2007, the International Campaign to Abolish Nuclear Weapons (ICAN) comprises more than 400 NGOs and has mobilised supporters and celebrities alike in its cause.

It was a key player in the adoption of a historic nuclear weapons ban treaty, signed by 122 countries at the UN in July.

But the accord was largely symbolic because none of the nine countries known or suspected to have nuclear weapons put their names down. It also still needs to be ratified before entering into force.

The United States, Russia, Britain, France, China, India, Pakistan, Israel and North Korea are all thought to possess nuclear weapons.

Speaking to reporters in Geneva, ICAN's head Beatrice Fihn said Trump's movements over North Korea and Iran showed the clear danger posed by nuclear arms.

"The election of President Donald Trump has made a lot of people feel very uncomfortable with the fact that he alone can authorise the use of nuclear weapons," she said, adding that the US leader had a track record of "not listening to expertise".

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But Washington reiterated Friday that it had no intention of signing the treaty, even though it remained committed to "creating the conditions for nuclear disarmament."

"This treaty will not make the world more peaceful, will not result in the elimination of a single nuclear weapon, and will not enhance any state's security," a State Department spokesman told AFP.

- Stockpiles falling -

Although global atomic stockpiles have plummeted -- from around 64,000 weapons in 1986 at the height of the Cold War to about 9,000 in 2017, according to the Bulletin of Atomic Scientists (BAS) -- they remain a global concern.

NATO, which has three of the world's nuclear powers in its ranks and which opposed the weapons ban treaty, welcomed "the attention given to the issue" by ICAN's win.

But the alliance's secretary-general Jens Stoltenberg said in a statement that "the conditions for achieving nuclear disarmament are not favourable today".

The survivors of the bombing of Hiroshima and Nagasaki, however, congratulated ICAN.

"We want to work together so that the nuclear disarmament treaty can be signed as soon as possible," said Shigemitsu Tanaka, head of the Nagasaki Atomic Bomb Survivors Council.

- 'Unspeakable horror' -

Friday's award comes as a global nuclear deal with Iran is under increasing pressure from Trump.

The agreement struck in 2015 between Iran and world powers drastically curbed Tehran's nuclear enrichment capability in return for a lifting of punishing economic sanctions. Iran denies ever pursuing a bomb, insisting its nuclear programme is for peaceful energy production only.

But Trump has threatened to bin the accord, and on Thursday criticised Iran's behaviour, telling military leaders in Washington that Tehran has "not lived up to the spirit of the agreement".

Trump is planning to decertify the deal, officials told AFP, potentially paving the way for renewed sanctions on Tehran.

Tensions have also soared between the US and North Korea, which has test-fired two missiles over Japan and conducted a string of apparent underground nuclear tests.

"This is a time of great global tension, when fiery rhetoric could all too easily lead us, inexorably, to unspeakable horror," ICAN said on Friday.

- 'World without nuclear weapons' -

The Nobel committee has rewarded anti-nuclear weapons drives on several previous occasions, honouring Soviet dissident Andrei Sakharov in 1975, the international non-proliferation group IPPNW in 1985, and Mohamed ElBaradei, then the head of the International Atomic Energy Agency, twenty years later.

UN chief Antonio Guterres praised ICAN's win, tweeting: "Now more than ever we need a world without nuclear weapons."

But Russia, which according to some counts has the world's largest atomic stockpile, said there was no alternative to "nuclear parity" in guaranteeing world peace.

More than 300 people and organisations were thought to have been nominated for this year's Peace Prize, including the UN's refugee agency UNHCR, Syria's White Helmets rescue service and Congolese doctor Denis Mukwege.

The Peace Prize, which comes with a gold medal and a cheque for nine million Swedish kronor (943,000 euros, $1.1 million), will be presented in Oslo on December 10, the anniversary of the death of its founder, Swedish philanthropist and dynamite inventor Alfred Nobel.