The U.S. on Monday sanctioned six senior Chinese and Hong Kong officials for "transnational repression" and further eroding the autonomy of Hong Kong, in the first major move by the Trump administration to punish China over its crackdown on the city.

"Beijing and Hong Kong officials have used Hong Kong national security laws extraterritorially to intimidate, silence, and harass 19 pro-democracy activists who were forced to flee overseas, including a U.S. citizen and four other U.S. residents," the State Department said in a statement.

In response, the U.S. is sanctioning six individuals who have "engaged in actions or policies that threaten to further erode the autonomy of Hong Kong in contravention of China's commitments, and in connection with acts of transnational repression," it said.