A slightly sheepish President Barack Obama accepted the 2009 Nobel Peace Prize as a "call to action" to the whole world to confront the global challenges before it, ranging from climate change to the threat of nuclear proliferation. But he made no attempt to conceal his astonishment at being selected.

Mr Obama used a Rose Garden appearance yesterday partly to deflect the attention from himself with humour and humility. "This is not how I expected to wake up this morning," he said, noting that his daughters were as quick to inform him it was also Bo the dog's birthday. Children, he said, "keep things in perspective".

The pre-dawn news from Oslo seemed to affirm the strong message of tolerance and dialogue that Mr Obama has proffered since before he was elected, but also threatens to heighten the burden of expectations on him. He indeed warned that much of what he aspires for will not be achieved in his presidency - or even his lifetime.

The announcement in the Norwegian capital drew gasps from assembled reporters. There were some expressions of shock, even disapproval, from a smattering of world figures, many sharing a theme that Mr Obama has won the prize too soon considering his goals have not borne much fruit.

But there was also a mild whiff of embarrassment at 1600 Pennsylvania Avenue. Rahm Emanuel, the chief of staff, conceded that his boss winning the Nobel Peace Prize had not been discussed once. David Axelrod, his political aide, had not even known that he had been nominated for it. When a reporter told Mr Axelrod that many people around the world were stunned, he replied: "As we are."

Mr Obama is only the third sitting US president to receive the peace prize, the other two being Woodrow Wilson in 1919 and Theodore Roosevelt in 1906. Jimmy Carter won it in 2002, two decades after leaving the White House. The 44th President was asleep when the call came from his spokesman Robert Gibbs. "To be honest, I do not feel that I deserve to be in the company of so many of the transformative figures who've been honoured by this prize," he said, "men and women who've inspired me and inspired the entire world through their courageous pursuit of peace".

He said he would collect the award in person at the ceremony in Oslo on 10 December and would donate the $1.4m prize money to charity.

The Norwegian Nobel Committee praised Mr Obama for "his extraordinary efforts to strengthen international diplomacy and co-operation between peoples", citing his fledgling push for nuclear disarmament and his outreach to the Muslim world.

As world reaction came in, offering praise and scepticism, some noted that the deadline for nominations for the prize fell just 11 days after Mr Obama was inaugurated.

Lech Walesa, former leader of the Solidarity union, which toppled Communism in Poland, was among those voicing doubts. "So soon? This is too soon. He has not yet made a real input. He is proposing, he is starting, but he still has to do it all," Mr Walesa, who won the prize in 1983, told reporters.