The action, coming one day after President Donald Trump put North Korea back on a list of state sponsors of terrorism, was announced by the U.S. Treasury in a statement on its website.
The new sanctions demonstrate the Trump administration's focus on hurting trade between China and North Korea, which the administration has said is key to pressuring Pyongyang to back away from its ambition to develop a nuclear-tipped missile capable of hitting the United States.
"This designation will impose further sanctions and penalties on North Korea and related persons and supports our maximum pressure campaign to isolate the murderous regime," said Treasury Secretary Steven T. Mnuchin.
The sanctions included blacklisting three Chinese companies, Dandong Kehua Economy & Trade Co., Dandong Xianghe Trading Co., and Dandong Hongda Trade Co., which the Treasury Department said have done more than $750 million in combined trade with North Korea.
The sanctions also blacklisted Sun Sidong and his company Dandong Dongyuan Industrial Co. In a June report, Washington think tank C4ADS said Sun Sidong's firm was part of an interconnected network of Chinese companies that account for the vast proportion of trade with North Korea.
U.S. authorities have repeatedly targeted companies and individuals from the Chinese city of Dandong, which borders North Korea, for alleged business ties to North Korea.
The new sanctions also hit several North Korean companies that send workers to countries such as Russia, Poland, Cambodia and China. United States authorities said they are seeking to cut off the money North Korea makes from the export of labour.
Along with targeting sources of weapons technology, the new sanctions marked the first time the United States sought to directly attack North Korea's everyday consumer trade, said Peter Harrell, a sanctions expert at the Center for a New American Security.
"What you are seeing here is we are sanctioning companies involved in ordinary trade," Harrell said. "That's the logical next step of the pressure campaign."
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