Armed Islamic Group (GIA): Extremist Islamic group in Algeria that has conducted civilian massacres as well as assassinations and bombings.
Aum Supreme Truth (Aum): Japanese cult created by Shoko Asahara that has used gas and chemical attacks in an attempt to win control of Japan.
Basque Fatherland and Liberty (Eta): Formed in northern Spain in 1959, Eta has carried out assassinations and bombings, killing more than 600 people.
Al Gama'a al Islamiyya: Largest militant group in Egypt, it specialises in armed attacks against Egyptian Government officials, but an attack on Luxor in 1997 killed 58 tourists.
Hamas (Islamic Resistance Movement): Formed in 1987 to overthrow Israel, it has carried out many suicide bombings against civilians and the military.
Harakat ul-Mujahidin (HUM): Militant Islamic group formed by Osama bin Laden's ally Fazlur Khalil in Pakistan. It attacks the Indian military and civilians in Kashmir.
Hizbollah (Party of God): Radical Shia group in Lebanon, thought to have carried out the suicide truck bombing of US Embassy and Marine barracks in Beirut in 1983.
Islamic Movement of Uzbekistan (IMU): Uzbekistani Islamic group that uses car bombs and hostage-taking to promote the creation of an Islamic state.
Japanese Red Army (JRA): During the 1970s the JRA carried out attacks worldwide. It is now reduced to a handful of hardcore members.
Al Jihad: Close supporters of bin Laden's al Qaeda, this Egyptian group specialises in attacks on high-level Egyptian Government officials. It claimed responsibility for assassinating President Anwar Sadat in 1981.
Kach and Kahane Chai: Two overlapping Israeli groups wanting to restore a biblical state of Israel. They threaten attacks on Arabs, Palestinians and the Israeli Government.
Kurdistan Workers' Party (PKK): Marxist-Leninist group of Turkish Kurds that has bombed hotels and kidnapped tourists.
Liberation Tigers of Tamil Eelam (LTTE): Tamil group conducting open war and terrorist acts such as suicide bombings in Sri Lanka.
Mujahedin-e Khalq Organisation (MEK or MKO): Largest Iranian dissident group, campaigning against the Iranian Government.
National Liberation Army (ELN): Marxist group in Colombia that uses mass kidnapping, hijacking, bombing, extortion and guerrilla warfare.
Palestine Islamic Jihad (PIJ): Has conducted suicide bombings in Israel, the West Bank and the Gaza Strip.
Palestine Liberation Front (PLF): Group led by Abu Abbas that specialises in aerial attacks. It was responsible for the attack on the cruise ship Achille Lauro in 1985.
Popular Front for the Liberation of Palestine (PFLP): Opposes negotiations with Israel and attacks Israeli and moderate Arab targets.
Popular Front for the Liberation of Palestine - General Command (PFLP-GC): Splinter group that has attacked Israel using hot-air balloons and motorised hang-gliders.
Al Qaeda: Osama bin Laden's group. It is blamed for attacks on the World Trade Center, Pentagon and US embassies as well as assassination attempts on Pope John Paul II and former President Bill Clinton.
Revolutionary Armed Forces of Colombia (FARC): Led by the ageing Manuel Marulanda, this group uses bombings, murder, kidnapping, extortion, hijacking and open warfare against the Colombian Government.
Revolutionary Organisation 17 November (17 November): Greek group that has assassinated US, British and Greek public figures and carried out rocket attacks.
Revolutionary People's Liberation Party/ Front (DHKP/C): Turkish group that has assassinated US military personnel and murdered foreign and Turkish workers.
Revolutionary People's Struggle (ELA): Greek group that has claimed responsibility for 20 bombings.
Sendero Luminoso (Shining Path): Created by former Peruvian university professor Abimael Guzman, the Shining Path has carried out indiscriminate bombings and murders since the 1980s, killing about 30,000 people.
Tupac Amaru Revolutionary Movement (MRTA): Peruvian group conducting campaign of bombings, kidnappings, ambushes and assassinations.
Many other terrorist organisations exist but fall outside the scope of the United States definition.
The list has three criteria. First, the organisation must be foreign, which would have meant that had any organised American group been behind the Oklahoma bombing, for example, would have been excluded.
Second, the organisation must be engaged in terrorist activity as defined by sections of the United States Immigration and Nationality Act.
Finally the organsiation's activities must threaten the security of US nationals or the national security of the United States.
This last criterion is broad, as it covers national defence, foreign relations or economic interests.
Asked why the IRA was not included, the Department of State acknowledged there was a strong body of evidence documenting that the IRA had been involved in terrorist activity.
But the Secretary of State had "taken note" of the IRA ceasefire and the decision by the British Government that the ceasefire was "genuine in word and deed".
The department said the peace process continued but "we will continue to monitor closely the activities of all paramilitary groups".
Map: Opposing forces in the war against terror
Afghanistan facts and links
For coverage of the attacks on the United States, see:
Full coverage: Terror in America
