Family members said Khieu Samphan was stricken Tuesday, just a day after two of his colleagues from the brutal Khmer Rouge regime were arrested by the tribunal.
Prime Minister Hun Sen told reporters he had dispatched a helicopter to Pailin in northwestern Cambodia to bring Khieu Samphan to Phnom Penh where his health will be closely monitored. The former Khmer Rouge leader's daughter, Khieu Rattana, confirmed his arrival.
Khieu Samphan's wife, So Socheat, said he was slowly recovering and could speak more clearly, walk with some help and eat food after receiving home care from doctors in Pailin, the former Khmer Rouge guerrilla stronghold where the couple live.
Reach Sambath, a tribunal spokesman, said the tribunal was not involved in the government's decision to fly Khieu Samphan to Phnom Penh. He said the tribunal does not yet have jurisdiction over Khieu Samphan.
On Monday, authorities arrested Ieng Sary, the Khmer Rouge's ex-foreign minister, and his wife Ieng Thirith, the social affairs minister. Both were charged with crimes against humanity Tuesday. Ieng Sary was also charged with war crimes.
Khieu Samphan knew his arrest was imminent, said his daughter, Khieu Rattana, who added that she did not think this caused his stroke.
"He has been aware all along that he will be arrested. He is not concerned about it and said he is ready to go to the tribunal," she said.
His blood pressure has been brought down and he has regained normal movement in his arms and legs, said a nurse, who asked not to be named because he is not authorized to speak to the media.
So Socheat said her husband fainted and collapsed to the floor when he tried to get up from a hammock Tuesday evening.
"His mouth became twisted, and he was not able to pronounce any clear words," she said.
She said that when her husband regained consciousness he told the doctors present that he could not afford to pay any medical expenses if he were taken to a hospital for treatment.
U.S. Ambassador Joseph Mussomeli said the stroke indicated that Khieu Samphan was getting nervous about being arrested.
"Perhaps justice breathes down his neck and causes his stress," he told The Associated Press.
The 1975-79 Khmer Rouge regime was blamed for the deaths of some 1.7 million people from starvation, disease, overwork and execution. None of the group's leaders has yet faced trial.
The U.N.-assisted tribunal was created last year after seven years of contentious negotiations between the United Nations and Cambodia .
The arrests of the Khmer Rouge suspects have come almost three decades after the group fell from power, with many fearing the aging suspects might die before they ever see a courtroom. Trials are expected to begin next year.
Four have been arrested so far, including Ieng Sary and his wife.
According to prosecutors' documents made available to The Associated Press, the fifth suspect they are seeking to charge is Khieu Samphan.
Nuon Chea, the former Khmer Rouge ideologist, and Kaing Guek Eav, also known as Duch, who headed the Khmer Rouge S-21 torture center, were detained earlier this year on charges of war crimes and crimes against humanity.
Ieng Sary and his wife said they do not have money to pay for their legal fees and are seeking financial aid, the tribunal's defense support section said in a statement Tuesday.
But the appeal for financial assistance was disparaged by fellow Cambodians, who said the couple lived a relatively lavish life in a villa in the capital, Phnom Penh .