The UN-backed war crimes tribunal in Cambodia on Friday rejected requests for release by three former Khmer Rouge leaders currently in pre-trial detention, according to dpa. The three, who face charges of genocide, war crimes and crimes against humanity, are former head of state Khieu Samphan; former foreign minister Ieng Sary; and his wife, former social affairs minister Ieng Thirith. Neither Khieu Samphan nor his defence lawyers appeared in court Friday. The ruling follows requests filed by their lawyers against the court's November decision to extend their pre-trial detention for a third and final year. The court's investigating judges are to decide later this year whether there is enough evidence to prosecute them. Should the trial go ahead, as is expected, it is likely begin early next year. A fourth former leader - the movement's ideologue Nuon Chea, known as Brother Number Two - is also in pre-trial detention. All four are elderly, and there are fears that one or more could die before any trial concludes. They are being held for their alleged roles in the deaths of an estimated 1.7 million people from execution, disease, starvation and overwork during Khmer Rouge rule of Cambodia between 1975 and 1979. The case is due to be the second that the tribunal, known as the Extraordinary Chambers in the Courts of Cambodia, will hear. The first was heard last year, and saw the regime's chief executioner Duch tried for crimes against humanity and war crimes. A verdict is not expected in Duch's case until July at the earliest. The movement's leader Pol Pot, known as Brother Number One, died in 1998.