By Conor Humphries and Ian Graham
BELFAST, Jul (Reuters) - Twenty-two police were injured when Irish nationalists rioted in Northern Ireland overnight, burning cars and firing petrol bombs to protest annual marches by pro-British Protestant groups.
Police fired plastic bullets and used water cannon to control crowds of up to 200 people in several Roman Catholic areas of Belfast, a police spokeswoman said. Rioters hijacked a bus and burned a van and motorcycle.
Tens of thousands of Protestants began marches across the province on Tuesday to mark the 1690 victory of King William of Orange over Catholic King James at the Battle of the Boyne, which helped secure Protestant supremacy in Ireland.
Pipe bands and drummers from Scotland joined local groups decked in orange banners and British flags for the marches that Protestant groups say is a central part of their culture, but many Catholics say are provocative.
"It's a celebration, we don't want any trouble," said Eddie Whyte, 42, as he marched past Belfast City Hall. "If they are offended by the British flag, maybe they shouldn't be living in this country."
Three decades of fighting between mostly Protestant loyalists who want Northern Ireland to remain part of the United Kingdom and Irish nationalists, mainly Catholics, who want it to be part of a united Ireland tore the province apart during a three decade period known as the "Troubles."
A 1998 peace agreement paved the way for a power-sharing government of loyalists and nationalists. Violence has subsided, but police say the threat from dissident groups opposed to the peace deal is at its highest since the deal was signed.
Police appealed for calm and launched major security operations in several sectarian flash points in the city, including the Catholic Ardoyne area, where a march last year sparked three days of rioting.
A sit-down protest by residents early on Tuesday passed off without incident.
"We must not allow the progress that has been made to be thwarted by those who want to drag us back to the past," Northern Ireland's First Minister Peter Robinson said.
Clashes broke out overnight as Protestant youths lit hundreds of bonfires to mark the July 12 holiday. Many burned the Irish flag and posters of Catholic politicians, including the mayor of Belfast.
A bus was hijacked near Belfast's mainly Catholic Falls Road. The driver was dragged into the road and the passengers ordered off before it was crashed close to police officers.
Police said they were investigating reports that shots were fired during the disturbances.
In North Belfast, a bomb alert forced the evacuation of a number of homes for several hours, but no device was found.
(Reporting by Ian Graham and Conor Humphries, Editing by Carmel Crimmins)