The downing of Malaysia Airlines jet MH17 in eastern Ukraine may constitute a "war crime", the UN human rights chief Navi Pillaysays.
Ukraine and Western governments believe pro-Russian rebels shot down MH17, using a missile system supplied by Russia. All 298 people on board - most of them Dutch - died on 17 July.
Moscow and the rebels have blamed Ukrainian forces for the plane crash.
Dutch and Australian police are now heading for the crash site.
Heavy fighting in the area prevented the police going there earlier. They want to help secure the huge crash site - in rebel-held territory - so that plane wreckage and human remains can be examined by international crash experts.
Most of the bodies have been removed, many of them repatriated to the Netherlands.
"This violation of international law, given the prevailing circumstances, may amount to a war crime," Ms Pillay, the UN High Commissioner for Human Rights, said in Geneva.