The United States on Thursday imposed sanctions on two firms, one in Russia and one in China, for supporting North Korea's nuclear and missile programs.
The new sanctions target Russian-based Volasys Silver Star and China-based Yanbian Silverstar Network Technology Co, the US Treasury Department said on its website.
A North Korean national, Song Hwa Jong, was also sanctioned, it said.
"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.
Mnuchin warned companies across the globe "to take precautions to ensure that they are not unwittingly employing North Korean workers for technology projects."
The Trump administration has maintained pressure on Pyongyang through sanctions in an effort to convince North Korea to give up its nuclear weapons, which are a threat to the United States.
President Donald Trump met North Korean leader Kim Jong Un in June at a summit in Singapore where Kim agreed in broad terms to work toward denuclearisation of the Korean peninsula. North Korea has however given no indication it is willing to give up its weapons unilaterally, as the Trump administration has demanded.
Washington has also accused Russia of violating UN sanctions on North Korea by granting work permits to North Korean labourers despite Russia's denial of any such actions.
A North Korean national, Song Hwa Jong, was also sanctioned