The U.S. Treasury has introduced individual sanctions against six physical persons, including four Russian nationals, for commercial ties with North Korea, the U.S. agency said in a press release published on its website.

The sanction list includes Ruben Kirakosyan, Mikhail Pisklin, Andrey Serbin and Irina Huish.

The sanctions also affect the Russian company Gefest-M LLC and a number of firms domiciled in China, Singapore and Namibia, it said.

"It is unacceptable for individuals and companies in China, Russia, and elsewhere to enable North Korea to generate income used to develop weapons of mass destruction and destabilize the region. We are taking actions consistent with UN sanctions to show that there are consequences for defying sanctions and providing support to North Korea, and to deter this activity in the future," Treasury Secretary Steven T. Mnuchin said in a statement also published on the agency's website.

These latest sanctions target third-country companies and individuals that assist "already-designated persons who support North Korea's nuclear and ballistic missile programs", the U.S. Treasury said. Other activities subject to the U.S. Treasury's individual sanctions included "dealing in the North Korean energy trade, facilitating the country's exportation of workers, and enabling sanctioned North Korean entities to access the U.S. and international financial systems", it said.