A UN-backed tribunal court said Thirith passed away "at approximately 10.30 a.m. (0330 UTC) on August 22 in Pailin, Cambodia."

"She was released under a regime of judicial supervision. She remained under judicial supervision until her death," the statement from the Extraordinary Chambers in the Courts of Cambodia (ECCC) added.

Although the charges against her were never dropped, the case was suspended in 2012 after the court ruled she was unfit to stand trial due to progressive dementia.

Genocide

Thirith was one of the few women in the leadership of the Khmer Rouge movement. She was a sister-in-law of the movement's late supreme leader, Pol Pot and wife to Ieng Sary, the regime's former foreign minister, who died in 2013 at age 87.

The radical communist party seized power in 1975. Over the following four years, an estimated 1.7 million people in Cambodia died of starvation, exhaustion, lack of medical care or execution.

'Direct involvement'

According to documents from the ECCC, Thirith was not a member of the regime's powerful standing committee but did sit on its council of ministers as social affairs minister.

"leng Thirith was personally and directly involved in denying Cambodians even the most basic of healthcare during the regime's years in power," said Youk Chhang, director of the Documentation Center of Cambodia which researches the atrocities.

Thirith allegedly ordered purges of suspected traitors in her ministry who were sent to re-education camps, and was aware of the regime's killing of perceived enemies.

She also allegedly participated in the regime's regulation of marriage - including its orchestration of mass forced marriages - and remained a ardent supporter of the Khmer Rouge long after its demise in the 1990s.

ksb/bw (AFP, AP, dpa)