"The Obama Administration identifies Iran as a major threat to U.S. national security interests. This perception is generated by suspicions of Iran's intentions for its nuclear program-- heightened by a November 8, 2011, International Atomic Energy Agency (IAEA) report--as well as by Iran's support for militant groups in the Middle East and in Iraq and Afghanistan. U.S. officials also accuse Iran of helping Syria's leadership try to defeat a growing popular opposition movement, and of taking advantage of Shiite majority unrest against the Sunni-led, pro-U.S. government of Bahrain. In October 2011, U.S. officials accused Iran of plotting to assassinate the Saudi Ambassador to the United States."
CRS Report for Congress, RL32048