A United Nations human rights official is leaving his job over what he calls a "genocide" in Gaza that the UN has failed to stop.

Craig Mokhiber, director of the UN's New York Office of the High Commissioner for Human Rights, said in a letter that Gaza is a textbook case of genocide. 

Mokhiber, who said he lived in Gaza working on human rights for the UN in the 1990s, accused the United States, the United Kingdom and European countries of giving political and diplomatic cover for Israel’s alleged atrocities. 

In the letter, which began with a statement acknowledging it would be his last official communication in his position, Mokhiber wrote that after witnessing what happened in Rwanda, Bosnia, and to Rohingya civilians in Myanmar, the UN has repeatedly failed to stop genocide.

“High Commissioner, we are failing again,” he said in the letter sent to the UN’s human rights chief Volker Turk in Geneva. 

The UN Secretary-General press secretary said Mokhiber is retiring as of Tuesday. 

CNN has reached out to Mokhiber for comment

CNN's Tara John contributed reporting to this post.