Northern Ireland's First Minister Peter Robinson on Sunday called for peace as a police officer was hurt in the third night of disorder in Belfast, AFP reports.
"It's very important that this violence stops," said Robinson.
"It's very important that cool heads prevail in these circumstances and I hope people will obey the announcement and statement by the Orange Institution that people should desist from violence.
"The only kind of protest that is ever justifiable is a lawful and peaceful protest," he added.
The Police Service of Northern Ireland (PSNI) said one officer had been injured in Sunday's clashes.
Riot police fired baton rounds as hundreds of loyalist protesters threw petrol bombs and other missiles following a tense stand off.
But the clashes were not as serious as on the two preceding nights.
On the first night of trouble on Friday, 32 officers were injured and a leading politician was knocked unconscious by a brick.
Nigel Dodds, the member of parliament for North Belfast, was taken to hospital after being hit on the head with a brick while trying to calm the crowds down on Friday night. He was later discharged.
The trouble flared after police tried to enforce a decision by an adjudication body banning the Orange Order from marching through a Catholic republican area of Belfast.
On Saturday, seven officers were injured, but not hospitalised, after being attacked with petrol bombs by Protestant rioters in the Northern Irish capital.
About a thousand police officers from mainland Britain had been sent to Northern Ireland in anticipation of tensions over the traditional Twelfth of July parades.
That event is the climax of the Protestant Orange Order's marching season.
The July 12 parade marks the victory of Protestant king William III of Orange over the deposed Catholic king James II at the Battle of the Boyne in 1690.
It is a flashpoint for tensions between the Protestant and Catholic communities in the province, which was devastated by three decades of sectarian violence in the 1970s, 1980s and 1990s.
The 1998 Good Friday peace accords largely brought an end to the unrest, known as The Troubles, although sporadic violence and bomb threats continue.