Cambodian officials have inaugurated a memorial at the Toul Sleng Genocide Museum to remember at least 12,000 people tortured and killed at the site when it was a Khmer Rouge prison.

Buddhist monks chanted prayers at Thursday's ceremony, attended by Cambodia's deputy prime minister and representatives from the United Nations and the Khmer Rouge tribunal.

The museum, formerly a high school in Cambodia's capital, Phnom Penh, was turned into S-21 prison after the Khmer Rouge took power in 1975. Of the estimated 16,000 men, women and children who passed through its gates, only a handful survived.

An estimated 1.7 million people died as a resulted of the Khmer Rouge radical polices from 1975 to 1979.

The Buddhist stupa replaces a similar memorial that disintegrated inside the Tuol Sleng complex.