A former New York City police sergeant charged with acting as an illegal Chinese agent for allegedly intimidating a U.S.-based fugitive from China went on trial on Wednesday and argued he did not know that country's government was behind a private surveillance job he took.

Federal prosecutors in Brooklyn say Michael McMahon pressured a New Jersey resident, Xu Jin, to return to China to face bribery and embezzlement charges, one example of a global repatriation campaign by Chinese law enforcement known as "Operation Fox Hunt."

The case is the first of several involving alleged Fox Hunt schemes to reach trial in the United States, as officials crack down on what they term "transnational repression" on dissidents and fugitives by adversaries including China.