One of the former Khmer Rouge's highest-ranking leaders has been freed from detention in Cambodia after a war crimes tribunal declared her mentally unfit for trial.

The 80-year-old Ieng Thirith was driven out of the U.N.-backed tribunal's compound by family members Sunday.

The court said it would impose restrictions on her release after prosecutors appealed a decision this past week to free her without conditions.

Until the appeal is heard, Ieng Thirith must remain in Cambodia, inform authorities of her address and report to the court whenever it summons her.

Ieng Thirith was social affairs minister during the Khmer Rouge's 1975-79 reign that left some 1.7 million Cambodians dead.

The tribunal said she suffers from a degenerative illness, probably Alzheimer's disease, that left "no prospect" for her to face trial.