Police in Derry are investigating after petrol and paint bombs were thrown during unrest last night.
24 petrol bombs and six paint bombs were thrown in the area around the City Walls.
Up to 40 people were involved in the disorder.
A laser pen was also shone at a police helicopter, while bricks and bottles were thrown at police.
The PSNI is urging those responsible to "pull back" from this behaviour, and is asking anyone with information to come forward.
PSNI statement in full -
A large number of petrol bombs and paint bombs were thrown during disorder in the Bogside area of Derry/Londonderry last night, Monday 12 August
A total of 24 petrol bombs and 6 paint bombs were thrown in the streets in the vicinity of the City Walls, and police patrols came under attack from youths throwing missiles including bricks and bottles.
Between 30 and 40 people were involved in the disorder which lasted from early evening into the night. A small barricade was also erected and burned at Fahan Street.
A laser pen was also shone at the PSNI helicopter, endangering both the crew and local residents.
Superintendent Gordon McCalmont said: “This is the third night that the people of this city have had to put up with unwanted disorder and destruction. No one wants to see these despicable scenes on our streets.
Some of the those involved in last night’s trouble were extremely young teenagers and I have no doubt that this disorder is being orchestrated by much older people and that these youths are being used to attack police and significant symbolic sites around our City Walls.
I would urge those young people to pull back from this behaviour and I would also ask those with influence within our community to use that influence positively and help dissuade young people from participating in public disorder. It must be made clear to them that they are risking their safety and that of others, as well as running the risk of a criminal conviction which could have a long lasting impact on their future prospects.
We have gathered a significant amount of evidence over recent days and I am confident that arrests will follow. Anyone with information that could assist police can contact us by calling 101."