Six countries have declined to attend the Nobel Peace Prize ceremony for jailed Chinese dissident Liu Xiaobo.
The Norwegian Nobel Committee said the ambassadors who were not going were from China, Russia, Kazakhstan, Cuba, Morocco, and Iraq.
Committee secretary Geir Lundestad said they had given no reason for declining.
Mr Lundestad said Beijing had mounted an unprecedented campaign to sabotage participation in the ceremony, which will be held on 10 December.
"I don't know of any example where a country has so actively and directly tried to have ambassadors stay away from a Nobel ceremony," he said.
Earlier this month, China warned that there would be "consequences" if governments showed support for Liu Xiaobo at the award ceremony.
The government in Beijing says Mr Liu is a "criminal".
The 54-year-old dissident received an 11-year sentence last year for "inciting subversion" after drafting Charter 08 - which called for multi-party democracy and respect for human rights in China.
A spokesman for the Russian embassy in Oslo, Vladimir Isupov, said the ambassador would not be in Norway at the time of the award ceremony.
"It is not politically motivated and we do not feel we are pressured by China," he told Associated Press.
Every year the Nobel Committee invites all the ambassadors based in Oslo to the peace prize award. The deadline for reply was 15 November but it was extended by three days.
This year, Mr Lundestad said 36 ambassadors had accepted the invitation to attend the ceremony, six had declined and 16 had not yet replied.
But he conceded that China was not the only factor.
"There are always some ambassadors that don't come for some reason, and they don't have to say why," he said.
Of those who had not replied, Mr Lundestad said some had asked for more time.
"Several countries have to check with their home governments," he told Reuters. "This has become a delicate issue with some governments."
It also appears likely that the prize itself will not be handed out during the ceremony because no-one from Liu Xiaobo's family has said they can attend, the Nobel committee secretary says.
The $1.4m (£900,000) award can be collected only by the recipient or close family members.
Mr Liu's wife has been under house arrest since the award was announced and friends of the couple told AP that his brothers were under tight police surveillance.