Police have come under attack during a third night of trouble in Londonderry.
The disorder broke out in the Bogside area, close to the City Walls, and lasted from early evening into the night.
Youths threw dozens of petrol bombs, paint bombs, bricks and bottles at police patrols, while a barricade was erected and burned in Fahan Street.
A laser pen was shone at the PSNI helicopter, “endangering both the crew and local residents”, a spokesperson said.
Between 30 and 40 people were involved, including some “extremely young teenagers”.
Police said they believe the disorder “was orchestrated by much older people” and urged youths to “pull back” from taking part in it.
"This is the third night that the people of this city have had to put up with unwanted disorder and destruction,” the spokesperson continued.
“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.”
The spokesperson added: “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."