"The Obama Administration views Iran as a major threat to U.S. national security interests, a perception generated not only by uncertainty about Iran's intentions for its nuclear program but also by its materiel assistance to armed groups in Iraq and Afghanistan, to the Palestinian group Hamas, and to Lebanese Hezbollah. As of mid-2011, U.S. officials are increasingly critical of what they say is stepped-up Iranian support for Iraqi Shiite militias that have attacked U.S. forces, who are scheduled to leave Iraq by the end of 2011. To try to address the threat from Iran, the Obama Administration offered Iran's leaders consistent and sustained engagement with the potential for closer integration with and acceptance by the West in exchange for limits to its nuclear program. However, after observing a crackdown on peaceful protests in Iran in 2009, and failing to obtain Iran's agreement to implement an October 2009 tentative nuclear compromise, the Administration worked during 2010 and 2011 to increase economic and political pressure on Iran. Major sanctions were imposed on Iran by the U.N. Security Council (Resolution 1929), as well as related 'national measures' by the European Union, Japan, South Korea, and other countries. Additional measures designed to compel foreign firms to exit the Iranian market were contained in U.S. legislation passed in June 2010 (the Comprehensive Iran Sanctions, Accountability, and Divestment Act, P.L. 111-195)."
CRS Report for Congress, RL32048