The State Department announced Tuesday that it has determined North Korea used chemical weapons last year in the assassination of Kim Jong Nam, North Korean leader Kim Jong Un's half-brother. According to the State Department, the use of the chemical agent VX at the Kuala Lumpur airport was sanctioned by North Korea.

State Department spokeswoman Heather Nauert tweeted Tuesday that the U.S. "condemns use of chemical weapons to conduct an assassination."

US condemns use of chemical weapons to conduct an assassination. This public display of contempt for universal norms against chemical weapons use further demonstrates reckless nature of #NorthKorea & underscores we cannot afford to tolerate a North Korean WMD program of any kind. — Heather Nauert (@statedeptspox) March 7, 2018

It's unclear why the announcement was made Tuesday, especially since in the memo Nauret tweeted, it said the U.S. made the determination on Feb. 22, 2018. On Tuesday, President Trump said he is "optimistic" North Korea will give up its nuclear weapons.

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The State Department said it is imposing sanctions under the Chemical and Biological Weapons Control and Warfare Elimination Act of 1991. The determination, made by the department's international security and nonproliferation bureau, carries restrictions on U.S. foreign aid and financial and military assistance that North Korea's heavily sanctioned government is already subject to.

This image provided by Star TV on Feb. 15, 2017, of closed circuit television footage from Feb 13, 2017, shows a woman, left, at Kuala Lumpur International Airport in Sepang, Malaysia, who police say was arrested in connection with the death of Kim Jong Nam, the half brother of North Korean leader Kim Jong Un. AP

Kim Jong Nam died shortly after he was attacked on Feb. 13, 2017 by two women at the international airport. Malaysian officials found VX in swabs from Kim's face and eyes.

North Korea is believed to have provided chemical defensive equipment and technology to Syria and Libya in the past, and an upcoming report by a United Nations panel that monitors sanctions against the North says that in August 2016 the North transferred special resistance valves and thermometers known for use in chemical weapons programs in Syria. North Korean technicians continue to operate at chemical weapons and missile facilities in the war-ravaged Mid-east nation, according to details of the report obtained by The Associated Press.

The U.S. and other Western nations have accused Syria of using chemical weapons against rebel-controlled areas of the country, which the government denies.

North Korea on Thursday denied it was cooperating with Syria on chemical weapons. In a statement circulated by its diplomatic mission at the U.N. in New York, the North's foreign ministry said it "does not have a single record of developing, producing and stockpiling a chemical weapon."