The so-called First Lady of Cambodia\'s genocidal Khmer Rouge regime must be held in detention, the UN-backed genocide court has ruled. An earlier court decision said Ieng Thirith should be freed unconditionally after she was adjudged to be too ill to face trial with other leaders. The 79-year-old is thought to suffer from Alzheimer\'s disease and dementia. The three most senior surviving Khmer Rouge leaders are on trial for crimes against humanity. They include Ieng Thirith\'s husband Ieng Sary, who was the regime\'s foreign minister. Officials estimate that the Khmer Rouge killed up to 2.2 million people during its 1975-1979 rule. Under supreme leader Pol Pot, the regime tried to build a Maoist peasant utopia, but descended into genocide as paranoid leaders sought to eliminate anyone who threatened them. Ieng Thirith served as the regime\'s social affairs minister, and was arrested and charged with the other leaders. But medical experts declared her unfit to stand trial, and her release was ordered. However, the tribunal ruled late on Tuesday: \"The supreme court chamber concluded that the original ground for keeping the accused in provisional detention, namely to ensure her presence during the proceedings, remains valid and relevant.\" The judges added that she would be transferred to medical facility for treatment \"which may help improve her mental health to such an extent that she becomes fit to stand trial\". The other leaders on trial are Pol Pot\'s deputy, Nuon Chea, and Khieu Samphan, the regime\'s former head of state. All three deny the charges they face. The UN-backed court\'s first case was the trial of Duch, the former Khmer Rouge prison chief who oversaw the torture and execution of thousands of inmates at Tuol Sleng prison. He was convicted of crimes against humanity last year.