At least a dozen police officers and two civilians were wounded as Protestant extremists threw homemade grenades, gasoline bombs and other makeshift weapons in fury over a restricted Belfast parade.
Protestants clashed with police, British troops and hostile Catholic crowds in several parts of Belfast on Saturday, after authorities blocked the Orange Order -- the territory's major Protestant brotherhood -- from parading past a hard-line Catholic area on the disputed Springfield Road.
On the nearby North Circular Road, six 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 armored 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 yesterday, riot police equipped with body armor, 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 organizations, the Ulster Defense Association and the Ulster Volunteer Force, were involved in the Protestant violence. Both groups are supposed to be observing cease-fires in support of Northern Ireland's 1998 peace accord.
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.
On Belfast's Shankill Road, more than 1,000 people confronted police units, who responded with plastic-bullet volleys and water jets. A helicopter's spotlight overhead illuminated the mayhem.
At least two civilians were hospitalized with injuries, but given the scope and intensity of the clashes, many more were likely to have been hurt. Typically in Belfast riots, civilians who are injured while rioting try to avoid hospitals because they can be identified and arrested.
Protestant mobs began blocking key roads and intersections in Belfast after police blocked Orangemen from marching on most of the Springfield Road, a predominantly Catholic area with one isolated Protestant section. Police forced the Orangemen to march through a derelict industrial site to their Orange lodge, which overlooks the road.
British army engineers erected truck-mounted canvas screens in hopes of blocking Catholics' view of the parade. But several hundred Catholics gathered on the road, and some stood on their rooftops to observe the drum-thumping procession. Both sides shouted vulgar abuse at each other.
Each summer, Northern Ireland endures inflamed communal tensions because of mass demonstrations by the Orange Order, a legal organization that was instrumental in founding Northern Ireland as a predominantly Protestant state 85 years ago.