The Nobel Peace Prize committee is beginning its award ceremony, amid continuing anger from the Chinese government at this year's winner. There is an empty chair for dissident Liu Xiaobo, who is in jail in north-east China for political offences. China has waged a wide-ranging campaign to discredit the award in recent weeks. Ahead of the ceremony, the UN said it had information that China had detained at least 20 activists and was making efforts to block Western media. A further 120 cases of house arrest, travel restriction, forced relocation and other acts of intimidation have been reported. In his opening remarks, Nobel committee chairman Thorbjorn Jagland said: "The Nobel Nomination Committee has long believed there is a close connection between human rights and peace." There was a standing ovation from the audience in Oslo city hall. The BBC's Damian Grammaticas, outside Liu Xiaobo's home in Beijing, says uniformed and plainclothes officers are guarding the compound. Mr Liu's wife, Liu Xia, is under house arrest.