Hong Kong (CNN) More than 20 countries, including Japan and the United Kingdom, have issued a joint statement condemning China's mass detention of Uyghur and other minorities in the country's Xinjiang region.

In a letter to the United Nations High Commissioner for Human Rights, Michelle Bachelet, the group of 22 nations urged China to end its "mass arbitrary detentions and related violations" and called on Beijing to allow UN experts to access the region.

The letter marks the first major collective international challenge to China's ongoing policy in the far western border region, where experts estimate up to 2 million people have been detained in vast re-education style camps.

Beijing denies any allegations of torture or political indoctrination, and says the camps are "vocational training centers" designed to fight terrorism and combat Islamic extremism.

Read More