Image caption Ieng Thirith is accused of committing crimes against humanity

A former leading member of the Khmer Rouge has been released after the genocide tribunal in Cambodia ruled that she was unfit to stand trial.

Ieng Thirith, 80, is thought to be suffering from Alzheimer's disease.

Under the terms of her release, Ieng Thirith has had to register her address and surrender her passport and ID card.

She was the social affairs minister during the 1970s when the Khmer Rouge was blamed for the deaths of up to two million people.

She had been due to be released on Friday after the court decided that she suffered from "a progressive, degenerative illness" and that there was no prospect that she could be tried "in the foreseeable future."

Her release was delayed while prosecutors lodged an appeal to limit her freedom.

The measures are aimed at preventing her from fleeing the country and interfering with the ongoing trials of three other senior Khmer Rouge leaders.

Who were the Khmer Rouge? Maoist regime that ruled Cambodia from 1975-1979

Led by Saloth Sar, better known as Pol Pot

Abolished religion, schools and currency in effort to create agrarian utopia

Up to two million people thought to have died of starvation, overwork or by execution

Defeated in Vietnamese invasion in 1979

Pol Pot fled and remained free until 1997 - he died a year later

She must also report to the court whenever it summons her.

The conditions were provisional, the court said in a statement, and further restrictions could be imposed following an appeal hearing at a later date.

Ieng Thirith was collected from the UN-backed court by her children.

Top ranks

Officials estimate up to two million people died during the Khmer Rouge's 1975-1979 rule.

Under supreme leader Pol Pot, the regime tried to build a Maoist peasant utopia, but descended into genocide as leaders sought to eliminate anyone who they deemed posed a threat.

Image caption A group of journalists wait outside the UN-backed court

In November 2011, three top Khmer Rouge leaders - Nuon Chea, Khieu Samphan and Ieng Sary - went on trial for crimes committed during the regime's rule. All three deny the charges.

Ieng Thirith, who was Ieng Sary's wife and the most powerful woman among the Khmer Rouge top ranks, has also denied any wrongdoing.

However, prosecutors said she knew that people were dying from starvation and disease on collective farms, but did nothing to stop the brutality.

Her sister was married to the movement's leader, Pol Pot. He died in the late 1990s.

Only one senior Khmer Rouge figure has been convicted in connection with crimes committed under the regime.

Prison chief Duch, born Kaing Guek Eav, was jailed in 2010 for his role in running a notorious prison where thousands of inmates were killed.