The U.S. Department of Treasury on Thursday slapped sanctions on two new companies for involvement in exporting "forced labor" from North Korea. 

The department's Office of Foreign Assets Control said in a statement that it blacklisted Russian construction company Mokran LLC and Korea Cholsan General Trading Corporation, a North Korean company operating in Russia.

The Treasury said the two had engaged in, facilitated or been responsible for the exportation of forced labor from North Korea, including exportation to generate revenue for the North Korean government or the Workers' Party. 

The sanctions block any assets the named entities might hold under U.S. jurisdiction and ban U.S. companies and individuals from doing business with them. 

A 2017 UN Security Council resolution demanded that all countries send home North Korean workers by December 22 last year to stop them from earning foreign currency for North Korea's nuclear ballistic missile programs. 

Treasury Secretary Steven Mnuchin said in a statement that those countries still hosting North Korean workers must send them home.