Petrol bombs have been thrown at police after a suspicious object was found in the Creggan area of Londonderry.
The Police Service of Northern Ireland (PSNI) said that about 15 homes had been evacuated in the Creggan Heights area.
Police said it is “a complex operation” which is expected to continue throughout the night.
Up to 80 officers are taking part in a security search targeting dissident republicans group, the New IRA.
PSNI Assistant Chief Constable Mark Hamilton said petrol bombs and missiles had been thrown at police, and two young people had sustained burn injuries as a result of engaging in disorder.
“The reality is this type of disorder contributes to the complexity of the policing operation and presents a real risk of injury to those involved,” he said.
The PSNI called on parents to “come bring their children home” after young people gathered around the police operation.
Rathmore roundabout to Fanad Drive is closed, and diversions are in place.
SDLP leader Colum Eastwood described the attack on police officers as “brutal and sustained”.
“People in this community will not be held to ransom by those who want to hold us all back,” he said.
The search comes after the discovery of a mortar bomb in Strabane, County Tyrone, on Saturday, which police have blamed on the dissident republican group the New IRA.
The police said the searches in Creggan were related to the group.
“Our search today is focused on public safety and extinguish that threat to the community,” said PSNI Supt Gordon McCalmont.
“Community support is key in this, we have disrupted 10 attacks. A key element is community support while we tackle the threat pose.”