The U.S. is "terminating" a 1955 amity treaty with Iran that regulates economic and consular relations between the two countries.
Secretary of State Mike Pompeo made the announcement at a press conference on Wednesday, and National Security Adviser John Bolton reiterated it later in the day.
"This is a decision, frankly, that is 39 years overdue," Pompeo said.
Pompeo also commented on an International Court of Justice decision that came down on Tuesday, ordering the U.S. to ease up some of its sanctions against Iran. In particular, the U.N.'s highest court wanted the U.S. to make sure sanctions didn't affect humanitarian aid and civil aviation.
Back in July, Iran filed a lawsuit with the ICJ against the U.S., claiming America violated some of the terms of the 1955 treaty when it reinstated sanctions against Iran. Pompeo called the lawsuit "meritless." He defended the U.S.' previous assurances that it would make sure humanitarian aid isn't affected by sanctions.
Pompeo also said that the only way for Iran's government "to secure a bright future for its country is by ceasing their campaign of terror and destruction around the world."