Cambodia's Khmer Rouge court Friday delayed freeing the regime's former "First Lady", who has dementia, after prosecutors requested tighter conditions for the genocide suspect's release.
The UN-backed tribunal ruled on Thursday that the 80-year-old Ieng Thirith, who experts say suffers from Alzheimer's disease, was mentally unfit for trial and should walk free, though the charges against her remain.
The news dismayed many survivors of the brutal 1975-1979 regime, blamed for the deaths of up to two million people.
Prosecutors said that they "fully agree" with the court's decision, but "her release should not have been unconditional".
"The co-prosecutors consider that the trial chamber has the legal authority to consider and apply limited, reasonably necessary and proportionate restrictions on Ieng Thirith's liberty," they said in a statement.
They have asked the court to impose six conditions for her release, including weekly checks by authorities and that she give up her passport.
Judges said on Thursday that Ieng Thirith would be incapable of remembering or adhering to any conditions, though they stipulated she should not interfere in the case in any way and should remain in Cambodia.
Ieng Thirith, the ex-social affairs minister and sister-in-law of the late regime leader Pol Pot, has always denied charges of war crimes, genocide and crimes against humanity.
Three other senior leaders of the regime, including her husband Ieng Sary, are currently on trial accused of the same atrocities.
The court's highest appeal body now has 48 hours to decide whether to accept the appeal. In the meantime, Ieng Thirith remains in the purpose-built detention facility at the court where she has been held since her 2007 arrest.
Leading Khmer Rouge researcher Youk Chhang, who lost many relatives during the regime's "Killing Fields" era, said the decision to release Ieng Thirith due to poor mental health was "a wake-up call" to the court.
"It has been taking too long to deliver justice to millions of victims in Cambodia," he told AFP.
Led by Pol Pot, who died in 1998, the Khmer Rouge dismantled modern society and wiped out nearly a quarter of the population through starvation, overwork and execution in a bid to create an agrarian utopia.
One of the few women in the Khmer Rouge leadership, Paris-educated Ieng Thirith is believed to have been involved in some of the murderous movement's most drastic policies.
She remained a staunch defender of the regime long after its demise in the 1990s.
The court has so far completed just one case, sentencing former Khmer Rouge prison chief Duch to life in jail this year for overseeing the deaths of some 15,000 people.
The ongoing second trial of the three ex-leaders is seen as vital to healing wounds in the still-traumatised nation, but campaigners have voiced dismay at the slow progress of proceedings given the advanced age of the defendants.
The health of Ieng Sary, 86, is of particular concern. The frail former foreign minister is currently in hospital with fatigue.