Cambodia and the United Nations signed an agreement today to hold a genocide trial for former leaders of the Khmer Rouge, whose brutal rule claimed about 1.7 million lives.

Cambodia and the UN will miss “the last chance” to try Khmer Rouge leaders for crimes against humanity unless they ratify an agreement to establish a genocide court, the UN legal chief warned.

UN Security Council members have been trying to resolve a stand-off with the US over its demand for immunity for it troops from the new UN war crimes tribunal.