Three police officers were injured after shots were fired during serious disturbances in the North overnight, police said.
The officers were attacked as a crowd of about 200 people threw petrol bombs, stones and bottles in north Belfast. Their injuries are not thought to be serious.
Police said water cannon and baton rounds had to be used after the trouble began at around 11.45pm last night.
The trouble flared as police tried to separate people in the nationalist Broadway area from those attending traditional loyalist "Eleventh Night" bonfires in the nearby Donegall Road.
It came ahead of the wider July 12 Orange Order celebrations in the city.
Chief Superintendent Mark Hamilton said the rioters were intent on causing "mayhem and destruction".
He said: "These officers were doing their jobs, were policing their local community and have been attacked whilst doing so.
"This is utterly wrong and I condemn it in the strongest possible terms.
"Those involved in tonight's violence were intent on causing mayhem and destruction.
"We responded to this disorder immediately and officers put themselves in danger in order to restore normal and calm to the area for the residents who live there. No-one wants a return to this type of behaviour."
He added: "I am very grateful to those in the community who took personal risk to try and prevent disorder and help the police in very difficult circumstances.
"We have appealed for calm in the run-up to the Twelfth of July and we continue to do so. We would appeal to anyone with influence in the community to exert it to ensure that the next few days pass off without incident.
An investigation is now under way into the disturbances. Anyone with information should contact the Police Service of Northern Ireland on 0845 600 8000.