(CNN) Ambassadors representing 37 countries praised China for its "remarkable achievements in the field of human rights," just a day after a group of 22 other countries formally condemned Beijing for the mass detention of ethnic and religious minorities in the country's Xinjiang region.

The Thursday letter was the first major collective international challenge to China's ongoing policy in its far western border region, where experts estimate up to 2 million people have been detained in vast re-education style camps. Many of those detained are ethnic Uyghurs and Muslims.

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.

China's partners backed that claim in their Friday letter, claiming the signatories to the Thursday statement were politicizing human rights issues, according to China's state-run Xinhua news agency

In their letter, the 37 envoys commended China's efforts in "protecting human and promoting human rights through development," echoing a common refrain used in Chinese state media.