The US has imposed sanctions on a dozen Russian and Chinese companies and individuals it accuses of helping North Korea’s nuclear weapons programme.
Earlier this month, members of the UN Security Council, including Russia and China, voted for further sanctions against Pyongyang.
The US Treasury said the move would “increase pressure” on North Korea.
China responded swiftly, calling on the US to “immediately correct its mistake” of punishing its firms.
The US Office of Foreign Assets Control designated 10 companies and six individuals in its sanctions.
“[The] Treasury will continue to increase pressure on North Korea by targeting those who support the advancement of nuclear and ballistic missile programmes, and isolating them from the American financial system,” said Treasury Secretary Steven Mnuchin.
The action means American individuals and companies are no longer permitted to do business with these firms.
A series of missile tests by Pyongyang has increased tensions between North Korea and the US, with both sides engaged in a heated exchange of threats.
US President Donald Trump has threatened the isolated regime with “fire and fury like the world has never seen”, leading North Korea to respond with threats to launch missiles near the US island of Guam in the South Pacific Ocean.
In North Korea’s latest propaganda video released on Tuesday, an image of Mr Trump is shown at a cemetery which is apparently meant to be in Guam.
Vice-president Mike Pence is also pictured engulfed in flames.
US Secretary of State Rex Tillerson meanwhile has praised North Korea for “a level of restraint” it has shown recently in its weapons programmes. He said the move could pave the way for talks between the two sides “sometime in the near future”.
“We have had no missile launches or provocative acts on the part of North Korea since the unanimous adoption of the UN Security Council resolution,” Mr Tillerson said in a reference to sanctions agreed by the UN against North Korea earlier this month.
But such placatory words were not in evidence at a UN meeting in Geneva on Tuesday when envoys for the US and North Korea clashed. Both countries are technically still in a state of war since the 1950s.
North Korean diplomat Ju Yong Chol denounced “constant nuclear threats” from the US.
He added that “the measures taken by [North Korea] to strengthen its nuclear deterrence and develop inter-continental rockets is justifiable and a legitimate option for self-defence in the face of such apparent and real threats”.