The United States has expressed concern over China's "worsening crackdown" on minority Muslim groups in the far western province of Xinjiang, amid allegations of widespread human rights abuses.
Rights groups have accused Beijing of the systematic mass detention of tens of thousands of ethnic Uyghurs and other Muslims in political re-education camps without being charged or tried.
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The allegations have prompted a growing international outcry and calls for sanctions to be imposed on senior Chinese officials.
On Tuesday, US State Department spokesperson Heather Nauert said the US government was "deeply troubled" by the crackdown, saying there were "credible reports" of thousands being detained in detention centers since April 2017.
"Some of those disproportionate controls on ethnic minorities -- expressions of their cultural and also their religious entities -- have the potential also to incite radicalization and the recruitment of violence," she told reporters during a press briefing.
Asked whether or not the US was considering economic sanctions against Chinese officials accused of overseeing the policies, Nauert acknowledged the State Department had received a letter from members of Congress on the issue, but declined to discuss details of any potential government action.
"We have a lot of tools at our disposal," she told reporters. "I'm not going to get ahead of any potential activity that the US Government may take. It's the old standard line on sanctions, that we're not going to preview any sanctions that may or may not happen."
In August, a bipartisan group of US lawmakers called for Chinese officials involved in alleged human rights violations in Xinjiang to be sanctioned under the Global Magnitsky Act -- the 2012 law originally designed to freeze the assets of certain Russian government officials and businessmen accused of human rights violations.
"The detention of as many as a million or more Uyghurs and other predominately Muslim ethnic minorities in 'political reeducation' centers or camps requires a tough, targeted, and global response," they said in a letter to Secretary of State Mike Pompeo.
Chinese Foreign Ministry Spokesman Geng Shuang said Monday the measures in Xinjiang were necessary to "crack down on ethnic separatist activities and (violence) and terrorist crimes."
"I want to say that Xinjiang is enjoying overall social stability, sound economic development, and harmonious co-existence of different ethnic groups," he said at his daily press briefing.
Nauert's comments follow the release of a new report by Human Rights Watch (HRW) Monday detailing allegations of indefinite, arbitrary detention.
Speaking to former Xinjiang residents the authors of the HRW report claimed Muslim ethnic minorities were detained for anything as small as "using foreign communication tools such as WhatsApp."
"The detainees in political education camps are held without any due process rights -- neither charged nor put on trial -- and have no access to lawyers and family," the report said.
In the camps, the report alleged detainees were forced to repeat slogans praising the Chinese Communist Party and President Xi Jinping, as well as singing patriotic songs.
"If they resist, or officials deem they have failed their lessons, they are punished. They may be subjected to solitary confinement, not be allowed to eat for a certain period, or required to stand for 24-hour periods, among other punishments," said HRW researcher Maya Wang.
On Monday, the new United Nations Human Rights chief Michelle Bachelet became the latest high profile international figure to speak out against alleged human rights abuses in Xinjiang.
Calling the allegations against China "deeply disturbing," Bachelet said Beijing had to allow access to the region for impartial observers.
"In light of these reports, we would request the Government to permit access for the (UN) to all regions of China, and trust we will embark on discussion of these issues," she said.
History of oppression
It isn't the first time the Chinese government has been accused of oppressing minorities in Xinjiang or other parts of the country.
Like Tibet, Xinjiang -- which has a history of independent rule and largely non-Han Chinese population -- has always been viewed with some suspicion by the authorities in Beijing, fearful it could become a hotbed of separatist, or in its case, Islamist organizing.
In May, Chinese state media said more than a million local Chinese Communist officials were being sent to live with local families in Xinjiang. The Uyghurs were forced to welcome officials into their homes, where they were subjected to "political education."
One month later, in a submission to the UN Committee on the Elimination of Racial Discrimination, the Germany-based Uyghur Congress (WUC) said an estimated one million Uyghurs were in political indoctrination camps as of July.
But the Chinese government strongly denied the figures, saying there was no mass imprisonment or "arbitrary detention."
"Xinjiang citizens including the Uyghurs enjoy equal freedoms and rights," Hu Lianhe, a spokesman for China's United Front Work Department, told the UN panel.