The State Department announced Tuesday new sanctions against North Korea in response to their findings of the use of the illegal nerve agent VX in the 2017 death of Kim Jong Nam, the estranged brother of the country’s leader, Kim Jong Un.

Under the Chemical and Biological Weapons Control and Warfare Elimination Act of 1991, the U.S. concluded in February "that the Government of North Korea used the chemical warfare agent VX to assassinate Kim Jon Nam, in the Kuala Lumpur airport,” the department said.

Kim Jong Nam died on Feb. 13, 2017 after two women allegedly wiped VX on his face before fleeing the Malaysia airport. He stumbled around before eventually falling. CCTV footage also showed the two women accused of carrying out the attack walking in the airport and going into the restroom before the incident. They were both charged with murder. Four other North Korean men who fled the country on the same day were believed to be involved in the plot.

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The sanctions, which reportedly took effect Monday, top a mounting list already levied against the hermit kingdom.

“The United States strongly condemns the use of chemical weapons to conduct an assassination,” the State Department said. “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.”

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The announcement from the State Department follows earlier comments on Tuesday from President Trump, who said “the world is watching,” in response to North Korea’s promise not to use nuclear or conventional weapons against Seoul. The country also reportedly expressed a willingness to hold talks with the U.S. on denuclearization, a South Korea official said in a statement after meeting with the neighboring country.

“Possible progress being made in talks with North Korea,” Trump tweeted. “For the first time in many years, a serious effort is being made by all parties concerned. The World is watching and waiting! May be false hope, but the U.S. is ready to go hard in either direction!”

Fox News’ Katherine Lam contributed to this report.