Sources say French prosecutors are investigating four fashion retailers suspected of concealing "crimes against humanity" in China's Xinjiang region.

The probe is linked to accusations against China over its treatment of minority Muslim Uyghurs, including forced labour.

China denies all accusations of abuse in the region.

The source told Reuters that Uniqlo France, a unit of Japan's Fast Retailing, as well as Zara owner Inditex, France's SMCP and footwear brand Skechers were the subject of the investigation.

France has a Central Office to Fight Crimes against Humanity, Genocide and War Crimes.

Inditex said it rejected the claims.

SMCP said it would cooperate with the French authorities to prove the allegations false.

Fast Retailing said in a statement from Tokyo that it had not been contacted by French authorities, and that none of its production partners are located in region.

Skechers said it does not comment on pending litigation.

United Nations experts and rights groups estimate over a million people have been detained in recent years in a vast system of camps in China's western Xinjiang region.

Several Western brands including H&M, Burberry and Nike have been hit by consumer boycotts in China after raising concerns about the reports.