The United States is imposing new sanctions against Iran, targeting its national airline and a major Iranian port company.

The U.S. Treasury Department announced the moves on Thursday against Iran Air and Tidewater Middle East Company and three other firms. The Obama administration says the entities are targeted because of illegal shipping activity and weapons movements.

The United States and its allies, as well as the United Nations, have already hit Iran with several rounds of sanctions for pursuing nuclear weapons technology and over human rights violations.

Earlier this month, the U.S. froze the assets of the Islamic Revolutionary Guard Corps, the paramilitary Basij and the Law Enforcement Forces also called Iran's national police. The moves were designed to crack down on human rights abuses by Iran's security forces.

Late last year, the U.S. blacklisted 10 companies and five individuals accused of helping Tehran develop nuclear weapons.

U.S. law prohibits Americans and U.S. businesses from doing business with sanctioned entities.