Dissident republicans have been blamed after six shots were fired at police officers in Londonderry, in what has been described as a "blatant bid to murder police officers".
The attack follows several nights of disorder in the Bogside area.
Police say petrol bombs were thrown in the vicinity of the city walls and at police patrols.
Chief Inspector Neil Beck said: "For a fourth consecutive night police officers dealt with violence and disorder.
"Around 16 petrol bombs and five paint bombs were thrown and, in what can only be described as a blatant bid to murder police officers, shots were fired at police close to our city's walls."
He added: "Police officers should not be targeted under any circumstances and their lives should not be put in danger by simply doing their jobs, attempting to keep people safe.”
Police and church leaders have appealed for calm in the area.
A number of males have been charged in connection with the disorder over previous evenings.