Police were attacked by youths in the Bogside area of Derry during a third night of disorder in the area.
Officers say between 30 and 40 people were involved in the trouble and a total 24 petrol bombs and 6 paint bombs were thrown in the streets.
A laser pen was also shone at a PSNI helicopter in the area "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."
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