Protestants clashed with police, British troops and hostile Catholic crowds in several parts of the Northern Ireland city of Belfast on Saturday after authorities blocked the Orange Order - the territory's major Protestant brotherhood - from parading past a hardline Catholic area on the disputed Springfield Road.
On the nearby North Circular Road, a half-dozen officers were injured by flames and shrapnel when masked Protestants hurled several homemade grenades, called "blast bombs", and gasoline-filled bottles at police lines.
Officers there took cover behind their armoured vehicles after hearing bursts of automatic gunfire. In east Belfast, police said another half-dozen officers suffered mostly superficial injuries as they kept apart rival Catholic and Protestant mobs.
In rioting that ran from Saturday afternoon until early Sunday, riot police equipped with body armour, shields and flame-retardant boiler suits repelled the attackers with British-style plastic bullets - blunt-nosed cylinders also known as baton rounds -and mobile water cannons.
Rioting spread at nightfall to Ballyclare and Newtownabbey, two predominantly Protestant suburbs of Belfast. Several buildings on Belfast's northern outskirts were also set on fire.
Police said members of two outlawed organisations, the Ulster Defence Association and the Ulster Volunteer Force, were involved in the Protestant violence.
Both groups are supposed to be observing ceasefires in support of Northern Ireland's 1998 peace accord.
Police blamed Orange Order
leaders for the disturbances
But the commander of Northern Ireland's police force, Chief Constable Hugh Orde, said Orange Order leaders had inspired the mob violence. Trouble flared at several major roads and intersections where Orange leaders had instructed members and supporters to stage sit-down protests.
"The Orange Order must bear substantial responsibility for this. They publicly called people on to the streets. I think if you do that, you cannot then abdicate responsibility," Orde said.
Each summer, Northern Ireland endures inflamed communal tensions because of mass demonstrations by the Orange Order, a legal organisation that was instrumental in founding Northern Ireland as a predominantly Protestant state 85 years ago.
Over the past decade, Catholic hardliners led by Sinn Fein, the Irish Republican Army-linked party, have violently opposed Orange parades that pass near Catholic areas.
Britain in 1997 formed a Parades Commission that has imposed restrictions on most of the disputed parades.