US President Barack Obama has been awarded the 2009 Nobel Peace Prize.
The Nobel Committee said he won it for "his extraordinary efforts to strengthen international diplomacy and co-operation between peoples".
The committee highlighted Mr Obama's efforts to support international bodies and promote nuclear disarmament.
Mr Obama's spokesman said the president was "humbled" to have won the prize. He said he woke Mr Obama up with the news early on Friday.
There were a record 205 nominations for this year's peace prize. Zimbabwean Prime Minister Morgan Tsvangirai and Chinese dissident Hu Jia had been among the favourites.
There was widespread surprise at the committee's decision. While world leaders were largely supportive of the award, thousands of people have contacted the BBC with more sceptical views.
Of thousands of comments received by the BBC, an estimated 75% expressed surprise at the award. Some said awarding the prize to Mr Obama was plain wrong, others that the decision had come too soon, before he had made any concrete foreign policy achievement.
The Nobel laureate - chosen by a five-member committee - wins a gold medal, a diploma and 10m Swedish kronor ($1.4m).
"Only very rarely has a person to the same extent as Obama captured the world's attention and given its people hope for a better future," the Norwegian committee said in a statement.
"His diplomacy is founded in the concept that those who are to lead the world must do so on the basis of values and attitudes that are shared by the majority of the world's population."
Asked why the prize had been awarded to Mr Obama less than a year after he took office, Nobel Committee head Thorbjoern Jagland said: "It was because we would like to support what he is trying to achieve".
"It is a clear signal that we want to advocate the same as he has done," he said.
He specifically mentioned Mr Obama's work to strengthen international institutions and work towards a world free of nuclear arms.
'New climate'
Reaction to the committee's decision from around the world was swift and varied.
Mohamed ElBaradei, the head of the UN's nuclear watchdog, the IAEA, said he could not think of anyone more deserving of the award.
"In less than a year in office, he has transformed the way we look at ourselves and the world we live in and rekindled hope for a world at peace with itself," Mr ElBaradei said.
At the other end of the spectrum, Taliban spokesman Zabihullah Mujahid told the Reuters news agency the award was ridiculous.
"The Nobel prize for peace? Obama should have won the 'Nobel Prize for escalating violence and killing civilians'," he said.
Since taking office in January, President Obama has pursued an ambitious international agenda including a push for peace in the Middle East and negotiations over Iran's nuclear programme.
But critics say he has failed to make breakthroughs. Domestically, Mr Obama has been working to tackle an economic crisis and win support for healthcare reform.
Some said they saw the prize as a way of encouraging the US leader early in his presidency.
"It is an award that speaks to the promise of President Obama's message of hope," said Archbishop Desmond Tutu of South Africa, a former winner.
French President Nicolas Sarkozy said the award confirmed "America's return to the hearts of the people of the world".
The statement from the Nobel Committee said Mr Obama had "created a new climate in international politics".
"Multilateral diplomacy has regained a central position, with emphasis on the role that the United Nations and other international institutions can play," it said.
The committee added that the US was now playing a more constructive role in meeting "the great climatic challenges" facing the world, and that democracy and human rights would be strengthened.
Mr Obama is the first US president to win the prize since former US President Jimmy Carter in 2002. Former vice-president Al Gore shared the prize in 2007.
Among earlier US leaders, Theodore Roosevelt won the prize in 1906 and Woodrow Wilson won it in 1919.
The Nobel prize was invented by the Swedish industrialist and inventor of dynamite Alfred Nobel, and was first awarded in 1901.
He designated the parliament in Norway, which at the time was united with Sweden, to elect the peace prize committee. Swedish academies are responsible for other prizes.
The prize-giving ceremony for the peace award is due to take place on 10 December in the Norwegian capital, Oslo.
