Sectarian rioting at a Londonderry interface is being organised on the internet and through mobile phones, residents believe.
Sectarian clashes have been occurring in Londonderry
Youths from the Irish Street and Top of the Hill areas have been involved in nightly clashes since Saturday.
On Wednesday night, about 30 people were involved in trouble in the area, which is in Derry's Waterside.
Stones were thrown at several police officers when they moved in to keep rival gangs apart.
Police believe there is an element of pre-planning.
Residents said, in the past, such behaviour has been organised on the internet and on mobile phones.
A man arrested over the trouble has been released on police bail.