Each year, the U.S. State Department issues a country report on terrorist activity around the world, including a chapter on State Sponsors of Terrorism. The following is the State Department's assessment of Iran in 2006:
"Iran remained the most active state sponsor of terrorism. Its Islamic Revolutionary Guard Corps (IRGC) and Ministry of Intelligence and Security (MOIS) were directly involved in the planning and support of terrorist acts and continued to exhort a variety of groups, especially Palestinian groups with leadership cadres in Syria and Lebanese Hizballah, to use terrorism in pursuit of their goals. In addition, the IRGC was increasingly involved in supplying lethal assistance to Iraqi militant groups, which destabilizes Iraq.Iran continues to be unwilling to bring to justice senior al-Qaida members it detained in 2003. Iran has refused to identify publicly these senior members in its custody on "security grounds." Iran has also resisted numerous calls to transfer custody of its al-Qaida detainees to their countries of origin or to third countries for interrogation and/or trial.
Iran maintained a high-profile role in encouraging anti-Israeli terrorist activity -- rhetorically, operationally, and financially. Supreme Leader Khamenei and President Ahmadi-Nejad praised Palestinian terrorist operations, and Iran provided Lebanese Hizballah and Palestinian terrorist groups -- notably HAMAS, Palestinian Islamic Jihad, the al-Aqsa Martyrs Brigades, and the Popular Front for the Liberation of Palestine-General Command -- with extensive funding, training, and weapons.
Iran pursued a variety of policies in Iraq, some of which appeared to be inconsistent with its stated objectives regarding stability in Iraq and with the objectives Iranof the Iraqi Transitional Government and the Multi-national Forces in Iraq. Senior Iraqi officials have publicly expressed concern over Iranian interference in Iraq, and there were reports that Iran provided funding, safe passage, and arms to insurgent elements.
State sponsors of terrorism pose a grave WMD terrorism threat. A WMD program in a state sponsor of terrorism could enable a terrorist organization to acquire a sophisticated WMD. State sponsors of terrorism and nations that fail to live up to their international obligations deserve special attention as potential facilitators of WMD terrorism. Iran presents a particular concern, given its active sponsorship of terrorism and its continued development of a nuclear program. Iran is also capable of producing biological and chemical agents or weapons. Like other state sponsors of terrorism with WMD programs, Iran could support terrorist organizations seeking to acquire WMD."
This information comes from the Department of State's April 2006 Country Report on Terrorism, Chapter 6, State Sponsors of Terrorism Overview