WASHINGTON—The U.S. Treasury Department on Thursday sanctioned two Russian and Chinese technology firms Washington said are front companies for North Korea generating illicit revenues for Pyongyang’s weapons programs.

The Treasury said China-based Yanbian Silverstar Network Technology Co. Ltd. and a sister company set up in Vladivostok, Russia, called Volasys Silver Star are managed and controlled by North Koreans and are earning millions of dollars for Kim Jong Un’s regime in violation of international sanctions.

The...