Major brands face a growing challenge to root out forced labor in Chinese supply chains, the top U.S. anti-human trafficking official said Friday, as the United States stepped up the blocking of imports of goods made in Xinjiang.

Ambassador-at-Large John Richmond said reports that forced labor by the Chinese government had spread beyond Xinjiang to other provinces complicated the process of due diligence for global firms.

“It is increasingly difficult for well-intentioned international companies to track exactly which products in their supply chain are made with forced labor,” Richmond told a Zoom call with journalists.