Interior spokesman Khieu Sopheak said on Thursday police would "take measures" to prevent Dream for Darfur holding a ceremony this weekend at Tuol Sleng, the Phnom Penh school that became the Khmer Rouge's main torture and interrogation centre.

Dream for Darfur has already held similar events in Chad, Rwanda, Armenia, Germany and Bosnia as part of a campaign to persuade China to push Khartoum into ending the violence in Darfur, where 200,000 people have been killed since unrest broke out in 2003.

Khieu Sopheak denied Cambodia's decision had anything to do with pressure from Beijing -- one of Phnom Penh's biggest donors -- saying the government was more worried about the politicisation of the Olympic symbol.

"According to its charter, the Olympics does not allow people to hold any forums which implicate or involve the Games in politics," he told Reuters. "This is nothing to do with Chinese aid."

An estimated 1.7 million people died under Pol Pot's 1975-79 Beijing-backed regime, which emptied the cities in bid to turn the country into a peasant utopia. Victims were tortured and executed, or died from starvation, disease and overwork.

China is a major supplier of military aid to Sudan and purchaser of its oil, giving Beijing the clout to push Khartoum to halt the violence in Darfur, critics say.

Many anti-Chinese pressure groups are using Beijing's hosting of the 2008 Olympics as an opportunity to bring pressure to bear.