The U.S. imposed more sanctions on North Korea on Thursday, slapping economic penalties on a China-based firm, its CEO and a Russia-based subsidiary.

The Treasury Department said the companies are actually controlled by North Korea, and the action "targets the revenue North Korea earns from overseas information technology (IT) workers."

It accused China-based Yanbian Silver Star Network Technology Co., and its Russia-based sister company, Volasys Silver Star, of violating U.S. sanctions by working to conceal the nationalities of North Korean IT workers.

The Treasury Department accused China Silver Star of having ties to the U.S. and UN-designated Munitions Industry Department, controlled by North Korea's ruling party. It said China Silver Star had earned millions of dollars of revenue, and its Russia-based subsidiary had revenue of hundreds of thousands of dollars in 2018.

China Silver Star's North Korean CEO, Jong Song Hwa, was also designated.

“These actions are intended to stop the flow of illicit revenue to North Korea from overseas information technology workers disguising their true identities and hiding behind front companies, aliases, and third-party nationals," Treasury Secretary Steven Mnuchin said in a statement.

"Treasury is once again warning the IT industry, businesses, and individuals across the globe to take precautions to ensure that they are not unwittingly employing North Korean workers for technology projects by doing business with companies like the ones designated today,” he added.

The designations are the latest effort by the Donald Trump administration to ramp up pressure on Pyongyang to fully and completely denuclearize.