At least eight police officers were injured during the annual Orange Order march by protestants in Belfast, after loyalists were stopped from passing a Catholic estate.
PSNI officers were pelted with bottles and other missiles, in response to which a water cannon and plastic bullets were deployed.
Thousands of Protestants, who support the union with Great Britain, hold marches every July 12 in the British-ruled part of Ireland to mark a 1690 victory by King William of Orange at the Battle of the Boyne, which sealed Protestant domination, a tradition Catholic Irish nationalists consider provocative.