"Because the actions and policies of the Government of Iran continue to pose an unusual and extraordinary threat to the national security, foreign policy, and economy of the United States, the national emergency declared on March 15, 1995, must continue in effect beyond March 15, 2011," Obama's notice says.

"Therefore... I am continuing for 1 year the national emergency with respect to Iran," it says.

Western powers suspect Iran of pursuing a secret nuclear weapons program but the Islamic Republic denies the accusations saying it needs nuclear power solely for civilian purposes.

The UN Security Council imposed a fourth round of sanctions against Iran in June 2010.