WASHINGTON, United States — The State Department is calling for the immediate release of three labour activists who investigated a Chinese company that produced Ivanka Trump shoes in China.

The Associated Press reported the arrest and disappearance of the men last week.

They worked for China Labour Watch, a New York-based nonprofit, and were investigating Huajian Group factories in the southern Chinese cities of Ganzhou and Dongguan.

The company has denied allegations of excessive overtime and low wages. It says it stopped producing Ivanka Trump shoes months ago.

State Department spokeswoman Alicia Edwards voiced concern Monday about reports that Chinese authorities detained Hua Haifeng and that activists Su Heng and Li Zhao are missing and presumed detained.

Edwards said labor activists have been instrumental in holding Chinese manufacturers accountable.