The overnight violence in Belfast saw missiles being thrown and petrol bombs ignited as Catholics took to the streets hours before Protestant Orangemen march in a traditional flashpoint 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 peace agreement in 1998, violence frequently breaks out around July 12 as Catholics try to prevent the marches from going ahead.