A lawyer says a Vietnamese activist has been sent to a drug rehabilitation center as an apparent punishment for her participation in anti-China protests.

Ha Huy Son says 47-year-old Bui Thi Minh Hang was detained Nov. 27 after joining a small protest in southern Ho Chi Minh City. The next day, Hang was transferred to Thanh Ha drug rehabilitation center in northern Vinh Phuc province, near Hanoi, without trial. She is to spend two years at the center.

Son said Wednesday that he's lodged a complaint with Hanoi Mayor Nguyen The Thao but has not heard back from him. His request to visit Hang was not met.

Hang was active in the weekly anti-China demonstrations that took place in the capital last summer after Hanoi accused Beijing of interfering with its oil exploration activities in the South China Sea.