China’s “arbitrary and discriminatory detention” of members of Uyghur and other predominantly Muslim groups in the country’s northwestern Xinjiang region “may constitute international crimes, in particular crimes against humanity,” the U.N. Human Rights Office said in a damning report released Wednesday.

“Allegations of patterns of torture, or ill-treatment, including forced medical treatment and adverse conditions of detention, are credible, as are allegations of individual incidents of sexual and gender-based violence,” said the much-anticipated report by outgoing U.N. High Commissioner for Human Rights Michelle Bachelet.

The report was hailed by human rights groups for adding credibility to long-running concerns over violations that some Western nations have labeled genocide. Japan’s top spokesman also expressed “grave concern” over the findings.