The US has determined Pyongyang used the chemical warfare agent VX to assassinate the half-brother of North Korean leader Kim Jong-un in Malaysia last year, and has imposed sanctions in response, the US State Department says.
The prohibitions appeared largely symbolic, such as sales to North Korea under the Arms Export Control Act and barring the export of national security-sensitive goods and technology to North Korea, which has no relations with the United States.
Mr Kim's estranged half-brother Kim Jong-nam died after two women smeared his face with a nerve agent inside a crowded airport terminal in Kuala Lumpur in February last year.
State Department spokeswoman Heather Nauert said in a statement the US Government made the formal determination about the use of VX on February 22 under the Chemical and Biological Weapons Control and Warfare Elimination Act of 1991.
The additional sanctions on Pyongyang went into effect on March 5 after the finding was formally published in the Federal Register, the official journal of the US Government, Ms Nauert said.
Secretary of State Rex Tillerson determined North Korea had "used chemical weapons in violation of international law or lethal chemical weapons against its own nationals," the department said in the Federal Register.
"The United States strongly condemns the use of chemical weapons to conduct an assassination," Ms Nauert said in the statement.
"This public display of contempt for universal norms against chemical weapons use further demonstrates the reckless nature of North Korea and underscores that we cannot afford to tolerate a North Korean WMD program of any kind."
Meanwhile, the Russian Foreign Ministry has condemned new US sanctions imposed on Pyongyang.
Maria Zakharova, a spokeswoman for the ministry, said any sanctions which were imposed unilaterally and not under the auspices of the United Nations were illegitimate.
Indonesian Siti Aisyah and Vietnamese Doan Thi Huong, are on trial on charges of murdering Kim Jong-nam.
Aisyah and Huong have pleaded not guilty to the murder charge, and said they were duped by North Korean agents into thinking they were playing a harmless prank for a hidden-camera TV show.