A senior police officer says dissidents are trying to drive police out of the Creggan area of Derry.
Officers came under attack there last night, with over 40 petrol bombs, while investigating a bomb found in a car.
They were deployed to the area yesterday, as part of an investigation targeting the new IRA.
Detectives are blaming the dissident group, after a bomb was left close to a police station in Strabane on Saturday.
Assistant Chief Constable Mark Hamilton has been speaking out: