More than 100 cops and many rioters were hurt in Northern Ireland early Friday as Roman Catholic protesters clashed with police after a day of Protestant marches.

The rioting was some of the province's worst in years.

The violence broke out hours after the Orange Order, Northern Ireland's biggest Protestant fraternal organization, staged hundreds of processions in villages, towns and cities to celebrate a Protestant military victory over Catholic forces in 1690. Some marches skirted close to Catholic areas; others featured virulent anti-Catholic rhetoric.

Protestants describe the parades as a celebration of their cultural heritage; Catholics call them a provocation.

As night fell, frustrations boiled over. When Protestant marchers passed by a run-down Catholic neighborhood in north Belfast, residents tried to block their path and wound up in a pitched battle with riot police. Rioters rained hundreds of firebombs and bricks on officers in riot gear, injuring dozens of them; police fought back with water cannons and 48 rounds of plastic bullets.

It was the worst fighting in the wake of the annual "Twelfth" parades — the highlight of Northern Ireland's flashpoint summertime "marching season" — that the province has seen in five years.

Police said at least 113 officers were hurt in fighting that erupted when about 200 Catholic protesters confronted police on the edge of Ardoyne, a low-income neighborhood of red-brick terrace houses.

Nineteen officers required hospital treatment, including two who were set afire by firebombs. By Friday morning, only two officers remained hospitalized, police said.

The province's police force, the Royal Ulster Constabulary, said Catholic protesters forced their way through a blockade set up to keep them away from the Protestant marchers. Catholics said police fired on them as they tried to stage a peaceful demonstration.

Pelted with bricks and firebombs, police responded with plastic bullets and jets from water cannons — the first time the crowd-control devices have been used on Belfast's streets in more than 20 years.

Late last month, the same area was the scene of Northern Ireland's worst sectarian clashes in three years.

Elsewhere, Catholic protesters clashed with marchers in the seaside town of Ballycastle, hurling rocks at one another before stoning police who tried to separate them.

Thursday's marches coincided with a push by British Prime Minister Tony Blair, his Irish counterpart Bertie Ahern and representatives from Northern Ireland's main political parties to defuse an acrimonious dispute centering on the outlawed Irish Republican Army's refusal to give up its hidden armaments.

The talks, which began Monday and took a one-day hiatus Thursday, were resuming Friday at a secluded mansion in the English Midlands.

In Washington, the U.S. State Department urged all parties to make a maximum effort to resolve outstanding disagreements over reform of the province's predominantly Protestant police force, further British troop pullouts and the scrapping of IRA weapons.

The Associated Press contributed to this report.