Former Khmer Rouge leader Khieu Samphan has been flown to the Cambodian capital to receive medical treatment. Officials say he is not under arrest. But he is expected to be arrested and tried by the country's genocide tribunal for his role in the deaths of almost two million Cambodians in the 1970's. Claudia Blume reports from Hong Kong.

The former Khmer Rouge head of state was flown to a Phnom Penh hospital by helicopter Wednesday from his home in the former rebel stronghold of Pailin, in northwestern Cambodia.

Prime Minister Hun Sen ordered the medical evacuation, saying he does not want people to blame the government if the former revolutionary leader dies.

Khieu Samphan, who is 76, reportedly suffers from high blood pressure, and reports Wednesday said he hurt himself in a fall. One report says he suffered a stroke.

Reports from Pailin said he was preparing to seek treatment in Thailand, but the Cambodian authorities stopped him from leaving the country.

Cambodia's United Nations-backed genocide tribunal has been investigating the Khmer Rouge era, and has arrested other former high-ranking members of the organization in preparation for trial. Khieu Samphan is expected to be one of those arrested and tried.

But tribunal spokesman Reach Sambath said Wednesday that Khieu Samphan is not yet under arrest.

"In his case, the court did not issue any court warrant to arrest him yet, so we don't have comment," he said.

Khieu Samphan's hospitalization highlights fears that the aged former Khmer Rouge leaders could die before being brought to trial. The group's top leader, Pol Pot, died in 1998.

It is widely expected, however, that assuming he does survive, Khieu Samphan will be prosecuted for his role in the Khmer Rouge's brutal rule of Cambodia from 1975 to 1979. Up to two million people were executed or died of starvation, disease and overwork when the ultra-radical communist group tried to turn the country into a classless agrarian utopia.

A total of four former Khmer Rouge leaders are already in detention, and have been charged with war crimes and crimes against humanity.

The group's former foreign minister, Ieng Sary, and his wife, Ieng Tirith, were arrested on Monday. The regime's second in command, Noun Chea, was detained in September. And in July, the court arrested Duch, the head of the Khmer Rouge's notorious torture center in Phnom Penh.

The court says Duch's trial, the first to be heard by the international genocide tribunal, is scheduled to start at the end of November.