Rioting by Catholics left 27 police injured in Northern Ireland, including three with gunshot wounds, officials said on Monday, ahead of the biggest day of Northern Ireland's marching season.
Missiles and petrol bombs were thrown in the night-time unrest as Roman Catholics took to the streets hours before Protestant Orangemen march in a traditional flashpoint event in the British province.
"This is utterly wrong and I condemn it in the strongest possible terms," said Chief Superintendent Mark Hamilton of the Police Service of Northern Ireland.
"Those involved... were intent on causing mayhem and destruction."
July 12 is the biggest day in Northern Ireland's marching season and sees Protestants mark Prince William of Orange's victory over the Catholic King James II at the Battle of the Boyne in 1690.
Despite the relative calm in Northern Ireland since a 1998 peace agreement, violence frequently breaks out around July 12 as Catholics try to prevent the marches from going ahead.
Twenty-one police officers were injured last year and there have been serious disturbances in previous years.
None of the officers injured this time were seriously hurt.
"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," said Hamilton.
"We have appealed for calm in the run up to the 12th 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."