Riots broke out at a parade in Belfast as loyalists protested a republican parade, with protesters throwing bricks and fireworks, paving stones and scaffolding poles at police, while officers fired back with plastic bullets.
Northern Ireland's Chief Constable Matt Baggott described the violence as "mindless anarchy" and "thuggery".
"I don't think there can be any excuses whatsoever for violence," Baggott said.
Eight people were arrested Friday night and police promised "many more will follow."
"I have no doubt whatsoever that significant custodial sentences will be handed down in the weeks and months that follow," Baggott said. "The prisons will be bulging, sadly."
A parade in County Tyrone, while met with protests, went forward without incident Sunday, even after calls to cancel the march as it was said to "glorify terrorism" and "cause great hurt" to those who died during the three-decades of the Troubles.
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