Belfast police chief vows mass arrests after Protestant militants attack officers, injure 56 Northern Ireland's police chief vowed Saturday to hunt down and imprison scores of Protestant militants after they attacked and wounded 56 officers protecting a parade by Irish Republican Army supporters. Friday night's outbreak of violence in downtown Belfast could be the first in a tense weekend involving disputed parades by both the Irish Catholic and British Protestant extremes of society. Senior police said Protestant extremists encouraged by social-media messages rallied to block the parade on Royal Avenue, Belfast's major shopping boulevard. Some wore British flags as capes or masks, and tore up scaffolding and pavement stones to attack police girded in full riot gear. Police responded by striking rioters with water cannons and 26 plastic bullets - blunt-nosed cylinders designed to deal punishing blows without penetrating the flesh. Several protesters could be seen staggering away from the confrontation zone with bloodied faces. Protestant politicians said security officials should never have authorized what they called a deliberately provocative march by Irish republican hard-liners opposed to Northern Ireland's peace process. After rival crowds of march supporters and opponents briefly outflanked police lines to trade salvos of rocks and bottles, march organizers abandoned their plan to parade past Belfast City Hall and diverted it back into Catholic turf. Britain's government minister for Northern Ireland condemned the Protestant mobs for "utterly disgraceful" behaviour. "Whatever people think about the merits of the parade or the views of the people taking part in the parade, the rule of law has to be respected," said Northern Ireland Secretary Theresa Villiers. Chief Constable Matt Baggott said Northern Ireland's prison population soon "will be bulging" as detectives used video footage to identify and arrest rioters. Baggott said seven people were arrested Friday night for attacks on police and the hijacking of cars, one of which was set on fire in the middle of the parade route. "You can be assured that many more (arrests) will follow," he said. He noted that more than 500 rioters, mostly Protestants confronting police in the streets of Belfast, already had been charged and convicted for earlier spasms of street violence in December, January and July. Baggott said the Protestant demonstrators lacked organization, self-respect or dignity. He said his officers had put their own lives on the line "to prevent that anarchy from spreading. Without that courage, many lives may well have been lost. This year's unusually protracted street trouble reflects rising working-class Protestant anger at Irish Catholic gains from the peace process. The U.S.-brokered Good Friday peace accord of 1998 sought to end IRA and other paramilitary violence, spur police reform and British military withdrawals, and forge a joint Catholic-Protestant government. Those goals have largely been achieved. But the supposed "unity" government continues to reflect fundamental divisions in Northern Ireland society. They have failed to reach a common position on each side's disputed marches. And as the Irish role in government and policing has risen, Protestant opposition to that changing face of authority has grown. The winter violence followed Catholic politicians" surprise decision in Belfast City Hall to curtail the flying of the British flag, a practice that had persisted year-round for a century. July's violence followed a decision by the government-appointed Parades Commission to block an annual Protestant parade by the Orange Order brotherhood from skirting an IRA power base in north Belfast, scene of heavy Catholic-police clashes following previous years" Orange parades. While the major IRA faction, the Provisionals, renounced violence and disarmed in 2005 after killing nearly 1,800 people in a failed bid to force Northern Ireland out of the United Kingdom, breakaway IRA factions have continued to mount bomb and gun attacks. Last year they formed a "new" IRA that does garner some support, and Friday night's march reflected that. But even the Provisionals, with their Sinn Fein party now at the heart of Northern Ireland's government, still justify and glorify past IRA violence, a fundamental sore point that shows no signs of easing. On Sunday a Sinn Fein-backed march honouring Provisional IRA members in the religiously divided town of Castlederg is proceeding, despite local Protestants" complaints that the IRA killed dozens in their community. One local politician compared it to permitting an al-Qaida parade through New York honouring the suicide attackers of 9-11. Sinn Fein insisted it would be dignified. The Parades Commission ordered the parade to avoid central Castlederg, but it still will pass other spots where the Provisional IRA killed Protestant civilians. Saturday's biggest parade is in Londonderry, Northern Ireland's second-largest city known for its 17th-century walled centre. There, an estimated 6,000 members from the city's main Protestant fraternal group, the Apprentice Boys of Derry, are marching alongside 145 bands from across Northern Ireland and Scotland. Police braced for potential nighttime clashes in Londonderry, a predominantly Catholic city where hostility to the annual parade in 1969 triggered days of rioting that forced Britain to deploy troops as peacekeepers. That fateful decision inspired the formation of the Provisional IRA. The Apprentice Boys commemorate the Protestant side's successful defence of the city in 1689, when an attempted handover of Londonderry to Catholic forces was prevented, in part, by teenage apprentices who bolted the city gates. A 105-day siege in which starving residents resorted to eating rats followed. Saturday's events involved marches atop the wall and a period-costume recreation of events 324 years ago.