China says Western diplomats exceeded their diplomatic roles by issuing a letter expressing concern about mass detentions in the northwestern province of Xinjiang.
A Foreign Ministry spokeswoman told reporters on November 15 that it would be "problematic" if the diplomats were attempting to put pressure on authorities in Xinjiang.
A group of foreign ambassadors to Beijing have asked in writing to discuss the situation in the province, where investigations by the United Nations revealed in August that an estimated 1 million Muslims from Xinjiang, mainly ethnic Uyghurs, were being held in "counterextremism centers" and millions more have been forced into reeducation camps.
Inmates and relatives say the detainees are forced to renounce their religion and culture while swearing fealty to President Xi Jinping and the ruling Communist Party.
The letter to the Chinese government has not been made public, but the Reuters news agency reported it was signed by 15 Western ambassadors, including the Canadian, British, French, German, and European Union envoys.
Chinese Foreign Ministry spokeswoman Hua Chunying said the letter was based on hearsay and violated the terms of the Vienna Convention governing diplomatic relations.
Last month, dozens of ethnic Kazakhs originally from Xinjiang held two separate public protests in Almaty, Kazakhstan, appealing to German and French officials for help in seeking the release of relatives from camps in China.
Also in October, Kazakhstan denied asylum to Sairagul Sauytbay, an ethnic Kazakh Chinese citizen whose court testimony helped expose "reeducation camps" in China.
Sauytbay is wanted in China for illegally crossing the border, but a Kazakh court in August refused to allow her extradition.
She fled Xinjiang in April and testified in the Almaty court that thousands of ethnic Kazakhs, Uyghurs, and other Muslims in Xinjiang are undergoing "political indoctrination" at a network of "reeducation camps."
Uyghurs are the largest indigenous community in Xinjiang, followed by Kazakhs, and the region is also home to ethnic Kyrgyz, and Tajiks.
Han, China's largest ethnicity, are the second-largest community in Xinjiang, which borders Afghanistan, Kazakhstan, Kyrgyzstan, Mongolia, Pakistan, Russia, and Tajikistan.
With reporting by Reuters and AP