PARIS—French prosecutors have opened an investigation into four fashion retailers suspected of concealing “crimes against humanity” in China’s Xinjiang region, a judicial source said on Thursday. The procedure is linked to accusations against China over its treatment of minority Muslim Uyghurs in the region, including the use of forced labour, the source said. China denies all accusations of abuse in the region. The source told Reuters Uniqlo France, a unit of Japan’s Fast Retailing, Zara owner Inditex, France’s SMCP and Skechers were the subject of the investigation, confirming a report by French media website Mediapart. “An investigation has been opened by the crimes against humanity unit within the anti-terrorism prosecutor’s office following the filing of a complaint,” the source said. France has a Central Office to Fight Crimes against Humanity, Genocide and War Crimes, founded in 2013. Inditex said it rejected the claims in the legal complaint, adding that it …