Mob violence against police officers in the North is being stoked up by individuals and social media, the chief constable said.
Forty roads were blocked last night and a policewoman guarding the offices of death threat MP Naomi Long was lucky to escape uninjured after loyalists broke windows on her car and threw a petrol bomb inside.
Eight nights of violence have followed Belfast City Council's decision to reduce the number of days it flies the Union flag on City Hall. The cross-community Alliance Party has been targeted after it agreed to the measure.
Police Service of Northern Ireland Chief Constable Matt Baggott said: "This is a phenomena of mob violence which has been stoked up by individuals and the social media."
He said it was fortunate nobody had been killed or seriously injured last night, and he praised police for doing a "magnificent" job.