The chairman of the Nobel prize committee has called for the immediate release of jailed Chinese dissident Liu Xiaobo, winner of the 2010 peace prize. There were two standing ovations at the ceremony in Oslo for Mr Liu, who was represented only by an empty chair. China has been angered by the award and has waged a campaign in recent weeks to discredit it. Nobel chairman Thorbjorn Jagland praised China for lifting millions of people out of poverty. He called it an "extraordinary achievement" but warned China that its new status as a leading world power meant Beijing "must regard criticism as positive". He said the Nobel committee was calling for Mr Liu to be freed immediately, saying: "He hasn't done anything wrong." For its part, China's foreign ministry condemned the ceremony as a "political farce". "We resolutely oppose any country or any person using the Nobel Peace Prize to interfere with China's internal affairs or infringe upon China's legal sovereignty," said the ministry in a statement. 'Quest for freedom' During the award ceremony, Norwegian actress Liv Ullmann read out a statement that Mr Liu had made in court during his trial in December 2009. "I, filled with optimism, look forward to the advent of a future, free China," said the statement. "For there is no force that can put an end to the human quest for freedom, and China will in the end become a nation ruled by law, where human rights reign supreme." Honouring the new laureate, Mr Jagland placed the Nobel diploma on the empty chair marking Mr Liu's absence. The Nobel chairman compared China's anger at the award to the outcry over peace prizes awarded to other dissidents of their times, including South African archbishop Desmond Tutu and the Burmese pro-democracy leader Aung San Suu Kyi. He said Mr Liu was dedicating his prize to "the lost souls from 4 June", those who died in the pro-democracy protests on that date in Tiananmen Square in 1989. "We can say (Mr) Liu reminds us of Nelson Mandela," he said. The former South African president received the Nobel Peace Prize in 1993. The UN says it had information that China detained at least 20 activists ahead of the ceremony. A further 120 cases of house arrest, travel restriction, forced relocation and other acts of intimidation have been reported. The BBC's English and Chinese language websites have been blocked, and BBC TV coverage was blacked out inside China during the ceremony. Mr Liu, one of China's leading dissidents, is serving an 11-year sentence in a jail in north-east China for state subversion. Police are stationed outside his home in Beijing where his wife, Liu Xia, is under house arrest.