China has angrily condemned the decision to award the Nobel Peace Prize to jailed Chinese dissident Liu Xiaobo.
The Beijing government summoned the Norwegian ambassador in protest. It called Mr Liu a "criminal", saying the award violated Nobel principles and could damage relations with Norway.
The Norwegian Nobel committee said Mr Liu was "the foremost symbol" of the struggle for human rights in China.
US President Barack Obama called for Mr Liu's immediate release.
"We call on the Chinese government to release Mr Liu as soon as possible," Mr Obama, last year's Nobel Peace Prize winner, said in a statement.
"Over the last 30 years, China has made dramatic progress in economic reform and improving the lives of its people, lifting hundreds of millions out of poverty.
"But this award reminds us that political reform has not kept pace, and that the basic human rights of every man, woman and child must be respected," Mr Obama said.
Other Western countries have also urged China to release Mr Liu.
Mr Liu, 54, was a key leader in the Tiananmen Square protests in 1989.
Last year he received an 11-year sentence for "inciting subversion" after drafting Charter 08 - which called for multi-party democracy and respect for human rights in China.
Announcing its 2010 peace prize in Oslo, the Nobel Foundation said: "Liu has consistently maintained that the sentence violates both China's own constitution and fundamental human rights."
It praised Mr Liu for his "long and non-violent struggle" and highlighted its belief in a "close connection between human rights and peace".
The citation described him as "the foremost symbol of this wide-ranging struggle for human rights in China".
Beijing quickly condemned the award, saying it could damage China-Norway relations.
Foreign ministry spokesman Ma Zhaoxu said: "Liu Xiaobo is a criminal who violated Chinese law. It's a complete violation of the principles of the prize and an insult to the peace prize itself for the Nobel committee to award the prize to such a person."
Later Norway said its ambassador in Beijing had been summoned to the Chinese foreign ministry.
"They wanted to officially share their... disagreement and their protest," a Norwegian spokeswoman said.
"We emphasised that this is an independent committee and the need to continue good bilateral relations," she added.
Unlike other Nobel prizes, which are administered in Sweden, the peace prize is awarded in Oslo by a committee appointed by the Norwegian parliament.
The prize is worth 10 million Swedish crowns ($1.5m; £944,000) and will be awarded in Oslo on 10 December.
In New York, UN Secretary General Ban Ki-moon said the award to Mr Liu was "a recognition of the growing international consensus for improving human rights practices and culture around the world".
German government spokesman Steffen Seibert said China should free him so he could attend the ceremony.
France's Foreign Minister Bernard Kouchner also welcomed the award and also called on China to release Mr Liu.
UN human rights commissioner Navi Pillay said the prize recognised a "very prominent human rights defender".
Mr Liu's wife, Liu Xia, said she was "so excited" by the award.
She told AFP news agency: "I want to thank everyone for supporting Liu Xiaobo. I strongly ask that the Chinese government release Liu."
Mrs Liu said police had informed her they would take her to Mr Liu's prison in the north-eastern province of Liaoning on Saturday so she could give him the news.