Nearly two dozen countries have called on China to halt its mass detention of ethnic Uighurs in the Xinjiang region, the first such joint move on the issue at the U.N. Human Rights Council, according to diplomats and a letter seen by Reuters.

U.N. experts and activists say at least 1 million Uighurs and other Muslims are held in detention centers in the remote western region. China describes them as training centers helping to stamp out extremism and give people new skills.

The unprecedented letter to the president of the forum, dated July 8, was signed by the ambassadors of 22 countries. Australia, Canada and Japan were among them, along with European countries including Britain, France, Germany and Switzerland, but not the United States, which quit the forum a year ago.