Police were attacked with stones and a shot was fired at officers
Rioting will not undo the progress made in the Northern Ireland peace process, Brian Cowen has said.
Ireland's prime minister was speaking after disturbances in Belfast which saw police shot at and pelted with missiles blamed on dissident republicans.
Mr Cowen said Northern Ireland was in a new era of partnership and condemned the violence in Ardoyne.
He said NI's democratic institutions were being challenged "by a tiny and unrepresentative group of people".
"They will not succeed," he said.
He was addressing the Senate (the Republic of Ireland's upper chamber) in Dublin.
In March dissident republicans killed two soldiers and a policeman.
Mr Cowen said after the murders Northern Ireland's leaders stood united in their determination that the region would not be pushed back into the "dark days of the past".
"That proved that we are truly in a new era in our history," he added.
"The rejection of this mindless violence and the united response of the political parties and of civic society sent a potent message that we will not allow a return to instability and violence.
"Yesterday's violent events were a further challenge to us all."
Assistant Chief Constable Alistair Finlay: Rioting is a "sinister development"
A senior policeman said children were involved in rioting in north Belfast, which he said was orchestrated by criminals.
Assistant Chief Constable Alistair Finlay said his officers had faced an "extraordinarily dangerous situation".
Twenty-one police officers were injured in Ardoyne and two blast bombs were thrown in violence after the passing of an Orange parade.
Mr Finlay said at least one gunman fired at police to try to murder them.
A BBC reporter saw a masked rioter fire a single shot from a handgun towards the police.
A loaded rifle was also handed into police after a group of children were seen playing with it.
Police said they fired 18 baton rounds during the trouble.
"It was dangerous, particularly from the sinister element of people amongst that crowd wanting to shoot police officers, wanting to kill police officers," Mr Finlay said.
"Wanting to derail whole processes through that, so it was an extraordinarily dangerous situation."
Council workers clean up following the rioting
The Real IRA has been blamed by Sinn Fein for the trouble.
However, the 32 County Sovereignty Movement, which is linked to the dissident group, denied this claim.
Ardoyne priest Father Gary Donegan said the trouble was started by outsiders.
"Myself and many people were looking at people last night that we'd never seen in the area before in our lives.
"It was as if people had been bussed into the area for this very purpose and that this was being very much orchestrated," he said.
Police promised a "rigorous investigation" to identify those who had taken part in the trouble.
Two more police officers were injured in other incidents across Northern Ireland.
Sinn Fein leader Gerry Adams condemned the violence and said the Orange Order should consider re-routing a small number of contentious parades, including those which pass Ardoyne.
"Why play into the hands of those who orchestrated last night disturbances?," he said.
"I would appeal to the Orangemen - they're not giving a victory to anyone if they just take an alternative route to where they want to go."
He also called for the leadership of the Orange Order to talk to Sinn Fein.
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