Barack Obama yesterday received the Nobel peace prize just 263 days after taking office, triggering praise and incredulity across the world over a decision that rewards him more for promise than achievement.

The US president said he was “surprised and humbled” by the Norwegian Nobel committee's decision, adding that he felt unworthy to be counted among the “transformative figures” of history who had previously won the prize.

However, the $1.4m award was also seen as something of a challenge to Mr Obama, with his critics arguing that he has so far failed to secure a clear foreign policy success.

The 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 reaching out to the Muslim world.

The award took the White House by surprise. Asked by a US media organisation to comment on the news, Robert Gibbs, the president's spokesman, e-mailed back the one word: “Wow.”

The decision was welcomed by world leaders. Angela Merkel, the newly re-elected German chancellor, said Mr Obama had rapidly changed the tone of international diplomacy towards dialogue. “There is still much left to do, but a window of possibility has been opened,” she said.

But others were scornful of the decision to reward a president who has yet to score any breakthrough in the Middle East or halt Iran's nuclear programme – and who may soon be sending thousands more troops to war in Afghanistan.

Lech Walesa, Poland's former president and a Nobel laureate himself, said it was too early to bestow the award on the 48-year-old US president.

“Who, Obama? So fast? For the time being Obama's just making proposals. But sometimes the Nobel Committee awards the prize to encourage responsible action.”