Terrorist organizations can be categorized as State-sponsored and subnational. State-sponsored terrorism has been most prominent in Middle Eastern countries such as Iran, Libya, and Syria. Subnational groups frequently seek political change and include Armenian, Irish, Palestinian, and Sikh groups. The Federal Bureau of Investigation (FBI) is the leading Federal agency for combating terrorism in the United States. Its mandate is to prevent terrorist acts before they occur and, should they occur, mount an effective investigative response. Effective intelligence is essential to the FBI's work. The FBI continues to improve its intelligence base through enhanced collection and analysis techniques and improved cooperation with other U.S. and foreign law enforcement agencies, security and intelligence agencies, and the private sector. Since 1985, the FBI has been involved in numerous investigations of terrorist incidents committed abroad, where U.S. citizens or interests have been targets. Law enforcement officials must develop counterterrorism response methods but preserve the rights of citizens. Such methods include diplomacy, economic sanctions, covert operations by intelligence entities, military intervention, and cooperative law enforcement operations.