HONG KONG — In a sweeping crackdown on opposition, police in Hong Kong on Wednesday arrested more than 50 pro-democracy figures for allegedly violating the stringent new national security law, according to political parties and local media.

Those arrested on suspicion of subversion included U.S. citizen John Clancey, an attorney and human rights advocate at the Ho Tse Wai & Partners law firm in Hong Kong and also chair of the Asian Human Rights Commission, a Hong Kong-based group that campaigns for greater human rights across the region.

A source close to the firm confirmed that he had been arrested and kept in police custody Wednesday.In a video published by the AFP news agency, Clancey is asked to react to his arrest and says, "Continue to work for democracy and human rights in Hong Kong."