U.S. Secretary of State Marco Rubio on Thursday condemned Thailand's return of at least 40 Uyghurs to China, where Washington says members of the Muslim group have faced genocide.

Human rights groups warned that the Uyghurs, who were held in Bangkok for more than a decade, will face mistreatment from Chinese authorities back in Xinjiang.

Dozens of Uyghur men detained in Thailand after fleeing China may have been secretly deported to their home country, activists and rights groups said on Thursday, warning they could face torture and imprisonment on their return.