A spat over the flag fluttering over a local government building might sound trivial. But in Northern Ireland, the decision to stop permanently flying the British flag outside Belfast City Hall has sparked some of the worst violence since the 1998 Good Friday peace deal.

Dozens of officers have been injured in attacks on police lines by furious protesters who, night after night, have thrown stones, bottles, fireworks, and, sometimes, Molotov cocktails -- violence that police say is orchestrated by the Ulster Volunteer Force, a pro-British paramilitary group.

Gunshots were heard Saturday, although police said later it appeared that blank rounds had been used. Monday night saw a mix of peaceful protest and riots during which police used water canon and fired plastic bullets, ITV News reported.