HONG KONG — An American citizen was among dozens of people arrested in Vietnam this week during protests against proposed special economic zones that have raised fears of Chinese encroachment.

The American, Will Nguyen, was visiting Ho Chi Minh City ahead of his graduation this summer from a master’s program at the University of Singapore, according to a statement from his family and friends.

Mr. Nguyen, 32, a Houston native who graduated from Yale, took part in protests on Sunday. He was “beaten over the head and dragged into the back of a police truck,” after the authorities moved to quash the demonstrations that day, according to the statement.

A video from the protests shows Mr. Nguyen, with blood smeared across his face, being dragged by a group of men. He is later shown standing in the bed of a pickup truck topped with emergency lights.