The police have been attacked with petrol bombs during trouble involving up to 50 masked people in Londonderry.

A senior officer said the disorder in the Waterside on Monday night was orchestrated and some of those involved had weapons.

Supt Sinead McIldowney described the trouble in the Knockwellan Park, Trench Road and Strabane Old Road areas as "absolutely disgraceful".

"We believe this disorder was orchestrated, which is shameful as many of those involved have been described as young people," she said.

"They are being used and exploited, and that is reprehensible."

The police said the trouble began around 19:30 BST when a group of "older and younger people", some with weapons, were seen going towards the playing fields in Knockwellan Park.

When police patrols arrived, the crowd dispersed in different directions but stayed in the general area.

Calm was restored at about 22:30 BST, the police said.

McIldowney said: "To the adults that were present last night and involved in the disorder, you are responsible for placing young people involved in danger.

"Last night there wasn't just a risk to their safety, but to their future if they end up with a criminal record."

She said the trouble did not reflect the good work that was being done in communities across the city and district.

"To the local community we know the disorder will have been very unsettling and frightening for many of you, but I want to reassure you will see a heightened and visible police presence in the area," she said.

The police have appealed for anyone with information to come forward.