Another program in rural Tibet, where workers are being transferred into military-style training centers, was reported by Reuters in September and defended by officials in Chinese-administered Tibet this week.
China's government has denied the mistreatment of the Uighurs in Xinjiang and the presence of forced labor in Tibet.
A representative for the Chinese Embassy in the United States said all workers in Xinjiang entered into contracts with employers and that the issue of forced labor there was a rumor created by anti-China media.
"Such a rumor has not a shred of fact in it," the Chinese representative said via email.
The US government's criticism of China comes at a time of bilateral trade tensions between the two countries.
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Separately on Thursday, US Customs and Border Protection (CBP) said it had detained the import of 32 cartons of women's leather gloves from Xinjiang on the suspicion they were made with forced labor.
CBP has issued 13 orders to block Chinese goods it suspected were made with forced labor in fiscal year 2020, including eight on goods from the East Asian country.
Some activists have asked for a broader detention order on goods from Xinjiang, but Richmond declined to say whether he was in favor of it.
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