Major retailers must stop sourcing from China's Xinjiang region due to the "grave risk of forced labour", a coalition of civil society groups says, amid mounting pressure on Beijing over its treatment of the Uighur Muslim minority.
More than 180 organisations urged brands from Adidas to Amazon to end sourcing of cotton and clothing from the region and cut ties with any suppliers in China that benefit from the forced labour of the ethnic Uighurs and other Muslim groups.
United Nations experts estimate that at least a million Uighurs and other Muslims are held in detention centres in Xinjiang.
China has denied mistreatment and said the camps offer vocational training and help to fight terrorism and extremism.
The United States this month hit senior Chinese officials with sanctions over alleged rights abuses against the Uighurs, and Britain and France have recently condemned their treatment.
While most fashion brands do not source from factories in Xinjiang, many of their supply chains are likely to be tainted by cotton picked by Uighurs that is exported across China and used by other suppliers, the rights groups said in a letter.
More than 80 per cent of China's cotton comes from northwestern Xinjiang, which is home to about 11 million Uighurs.
"Brands and retailers recognise there is a massive problem in the region, and that their supply chains are exposed to a grave risk of forced labour," said Scott Nova, head of the US-based Worker Rights Consortium (WRC), which signed the letter.
"We are cautiously optimistic that there will be commitments (from brands to pull out of Xinjiang) in the future," he added.
A spokesperson for the Chinese embassy in the United States earlier this month said the accusation of forced labour in Xinjiang was "both false and malicious".
The Thomson Reuters Foundation sent emailed questions to more than 30 leading global retailers about their supply chains in China and the origins of the cotton they sourced.
All the companies that responded - including Gap, Patagonia and Zara-owner Inditex - said they did not source from factories in Xinjiang, but the majority could not confirm that their supply chain was free of cotton picked from the region.
Japanese retailer Muji said it used cotton from Xinjiang but that independent auditors had found "no evidence of accusations of forced labour ... at their mills".