President Donald Trump has signed an executive order targeting Iran’s supreme leader and his associates with financial sanctions.
Mr Trump said the supreme leader is responsible for Iran’s hostile conduct.
He said the United States does not seek conflict with Iran but will continue to increase pressure on its Middle East adversary to prevent it from developing nuclear weapons and supporting militant groups.
The United States pulled out of a 2015 nuclear deal that world powers signed with Iran and has already applied crushing sanctions on the country’s economy.
The president said Monday’s action follows a series of aggressions by Iran, including the shooting down of a $100m US surveillance drone over the Strait of Hormuz.