This is stated on the White House website.
"The existence and risk of the spread of fissile materials suitable for use in weapons on the Korean Peninsula, as well as the actions and principles of the North Korean authorities continue to pose an extreme and exceptional threat to national security, foreign policy and the economy of the United States," the document says
It is noted that the sanctions regime was announced by presidential decree of June 26, 2008.
Earlier, US Secretary of State Mike Pompeo said that the United States is introducing new sanctions against Syria, in particular, they are aimed at Syrian President Bashar al-Assad and his wife.