The PSNI in Northern Ireland say a small group who came prepared for trouble instigated last night's violence in Belfast.
A group of Orange bandsmen and their supporters were attacked with golf balls, bottles and stones as they passed the nationalist area of Ardoyne.
18 police officers were injured and eleven other people were hurt including a 14-year-old girl whose arm was broken.
Police say they will investigate reported breaches by nationalist protestors of a Parade Commission ruling on the march.
Local residents also clashed with police, who sought to create a corridor between the marchers and nationalist residents. Water canon was used to disperse protestors.
The DUP MP, Nigel Dodds, claimed the fault lay with protestors. Gerry Kelly of Sinn Féin blamed the ruling on the march made by the Parades Commission.
