(CNN) An American citizen was detained in Vietnam while protesting a proposed economic zone law that could clear the path for Chinese investors, his family says.

William Nguyen, 32, from Houston "was beaten and dragged into the back of a police truck" on June 10 in Ho Chi Minh City, his family said in a statement.

Nguyen, a public policy graduate student, was visiting Vietnam before his graduation from the National University of Singapore when he joined the protests.

"As an American citizen and peaceful demonstrator, Will is entitled to be treated fairly, without fear of bodily and psychological harm," his family said. "He has the right to legal representation in accordance with international laws."

Video footage from the protests shows Nguyen, who had blood on his face, being dragged by a group of men down a street. The video also shows him standing up on the bed of a police pick-up truck.

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