Differences Between External and Internal Services
The objective of internal intelligence services is to obtain, compare and evaluate intelligence relevant to the internal security. The internal security strives to protect the state, the territory and the society from terrorism, espionage, sabotage, subversion, extremism, organized crime, production and smuggling of drugs etc.
The general objective of external intelligence services is to obtain, compare and evaluate intelligence relevant to the external security and the possibility to warn. Ensuring the external security requires the knowledge of threats, dangers and risks and also the probability of events, leading for instance to an attack. Thus it is necessary to have information about intentions, abilities and activities of foreign states, organizations, groups (or individuals) which impose a real or potential threat to the state and its interests.
Source: Petr Zeman - lectures, trainings and public speeches