Three men in their 40s are due to appear in court in Derry later charged with terror offences.
It follows the discovery of a home-made rocket in a car stopped in the city on Thursday night.
The men are charged with possession of explosives, conspiracy to murder and having articles for use in terrorism.
A 41-year-old man who was also arrested was released unconditionally. Police said the rocket was of a type used to attack armoured vehicles.