BANGKOK — An American citizen who was arrested at a peaceful demonstration in Vietnam this month said on state television that he regretted breaking the law and that he would not join such protests again.

Will Nguyen, 32, an American graduate student in Singapore, has been held since June 10, when he was grabbed and beaten by the police at an anti-China protest in Ho Chi Minh City.

Two videos posted on YouTube show him being dragged down the street by plainclothes officers holding his legs and an arm. One man comes up and strikes him. Another places an orange covering over Mr. Nguyen’s head.