The Trump administration on Tuesday slapped economic sanctions on 10 Chinese and Russian companies and six people for covertly assisting North Korea’s nuclear weapons and missile programs.

The Treasury Department announcement said the sanctions were imposed “in response to North Korea’s ongoing development of weapons of mass destruction, violations of United Nations Security Council Resolutions, and attempted evasion of U.S. sanctions.”

The sanctions represent the first time the U.S. government has cracked down on Chinese and Russian firms that have been facilitating North Korea’s development of nuclear arms and long-range missiles.

“Treasury will continue to increase pressure on North Korea by targeting those who support the advancement of nuclear and ballistic missile programs, and isolating them from the American financial system,” said Treasury Secretary Steven T. Mnuchin.