Hong Kong (CNN)China has committed "serious human rights violations" against Uyghur Muslims in its northwestern region of Xinjiang, which may amount to "crimes against humanity" according to a long-awaited report released Wednesday by the United Nations High Commissioner for Human Rights.

The detailed 45-page report, published just minutes before outgoing commissioner Michelle Bachelet's term in office came to an end at midnight Geneva time, had been repeatedly delayed, and its release vehemently opposed by China.

The report, which documented what it described as arbitrary and discriminatory detention of members of Uyghur and other predominately Muslim groups within the context of the government's "application of counter-terrorism and counter-'extremism' strategies," was hailed by rights groups as a groundbreaking moment in the effort to hold the Chinese government to account.

The report comes four years after a committee of UN experts called attention in August 2018 to "credible reports" that more than 1 million Uyghur and other Muslim minority peoples were interned in extrajudicial camps in Xinjiang for "re-education" and indoctrination.

China has fiercely denied committing rights violations. It has previously said it established such centers as a way to counter "extremism" in the region, and has since said the facilities were closed -- a claim the UN office said it could not verify.

According to the UN report, "the described policies and practices in (the region) have transcended borders, separating families and severing human contacts, while causing particular suffering to affected Uyghur, Kazakh and other predominantly Muslim minority families, exacerbated by patterns of intimidations and threats against members of the diaspora community speaking publicly."The Chinese government, which had repeatedly objected to the release of the report, responded in a 131 page document -- nearly three times the length of the report itself -- in which it decried the findings as "based on the disinformation and lies fabricated by anti-China forces."

Beijing's response was released by the Office of the United Nations High Commissioner for Human Rights (OHCHR) in tandem with its own report after China was given advance access to the document to review and respond.

Separately on Thursday, a spokesperson for the Ministry of Foreign Affairs said China "rightfully rejects" the report, which it called "invalid and illegal." The spokesperson also accused the Office of High Commissioner of being "reduced to the role of a hitman and an accomplice of the US and the West in their efforts to control developing countries."While the report was welcomed by some Uyghurs overseas and human rights activists, any move toward further investigation -- as called for in the report -- would need approval from UN member states in a body where China holds considerable