American residents, either citizens or people with legal status in Washington, are allegedly being held in detention camps in China's Xinjiang, media reports quoted sources in the US State Department.
There is, however, no exact number of how many American residents are being held, US-based media house CNN reported, adding that there were "a few".
A US official said he had a new, unconfirmed report about a California man whose father, a legal US resident, had not been heard from since returning to Xinjiang.
"He had legal status being here, travelled back to Xinjiang after being here with his son in California. And then has not been heard from since. And he's deeply concerned about whether, what his treatment is. He has a number of chronic illnesses, he's a 75-year-old man and an intellectual," Ambassador at Large for International Religious Freedom Sam Brownback said.
"Entire villages are being encased and people limited on their movement in and out, of the villages in that region that's occurring as well. The situation continues and in some cases appears to be escalating, not de-escalating," he added.
Last year, a report by the US State Department Human Rights estimated that China "arbitrarily detained 8,00,000 to possibly more than two million Uyghurs, ethnic Kazakhs, and other Muslims in internment camps designed to erase religious and ethnic identities".
The State Department on Thursday reiterated its travel advisory for US citizens going to China, warning specifically of "extra security measures in the Xinjiang Uigher Autonomous Region".
The Chinese government has defended these camps as a means of fighting, what they claim is a rising tide of extremism in Xinjiang.
It claimed that the camps are "vocational and educational training centres for counter-terrorism and de-radicalisation purposes".