'First lady' of Khmer Rouge ruled unfit for genocide trial September 13, 2012 -- Updated 0904 GMT (1704 HKT) Ieng Thirith pictured in 2010 before the Extraordinary Chambers in the Court of Cambodia (ECCC) in Phnom Penh. U.N. court in Cambodia upheld earlier diagnosis that Ieng Thirith has dementia Court: Experts say accused's cognitive impairment is 'likely irreversible' Three others, include Ieng Thirith's husband, face charges of crimes against humanity Khmer Rouge regime's four-year rule in the 1970s is blamed for 1.7 million deaths Hong Kong (CNN) -- The special court set up in Cambodia to try people accused of atrocities under the Khmer Rouge has ordered the release of the regime's "first lady," saying she's unfit to stand trial. Ieng Thirith, who served as minister for social affairs in the Khmer Rouge regime during the 1970s, had been accused of crimes against humanity, grave breaches of the Geneva Conventions, genocide, homicide, torture and religious persecution. However, proceedings against her were halted in November last year after the Extraordinary Chambers in the Courts of Cambodia decided she could not face trial as she suffered from dementia. After seeking further medical assessment, the court issued a statement Thursday confirming the earlier diagnosis that Ieng Thirith suffers from a "progressive, degenerative illness (likely Alzheimer's disease) and remains unfit to stand trial." Judge resigns from court trying Khmer Rouge crimes It added that medical experts confirmed that "all treatment options have now been exhausted and that the accused's cognitive impairment is likely irreversible." As a result, the court recognized she would be incapable of remembering or complying with any conditions -- but reminded her not to interfere in their investigations in any way and to remain in Cambodia. Khmer Rouge torture prison chief gets life sentence Ieng Thirith, 80, was one of four surviving leaders of the brutal regime facing prosecution -- the others being her husband Ieng Sary, the former Khmer Rouge foreign minister; Khieu Samphon, the nominal head of state; and Nuon Chea, the prime minister, also known as Brother Number 2. They remain on trial. The head of the Khmer Rouge, Pol Pot, was known as Brother Number 1. He died in 1998, long before the U.N.-backed court came into existence. He had previously been married to Ieng Thirith's sister, Khieu Ponnary. Under Pol Pot's leadership, the Khmer Rouge regime was responsible for the deaths of millions of ordinary Cambodians during a four-year reign of terror that was eventually halted in 1979 by invading Vietnamese forces. In 1975, the Khmer Rouge ordered people out of Phnom Penh, the capital, and other cities in Cambodia to work in the countryside. It is said to be responsible for about 1.7 million deaths, roughly a quarter of the population at the time. Its stated aim was to create a Communist utopia, but instead the regime forced Cambodians into what has been described as a living hell. CNN's Kocha Olarn contributed to this report.