Dissident republicans are being blamed for violence across Northern Ireland last night which left 21 PSNI officers injured.
The most serious clashes occurred in the Ardoyne area of north Belfast where nine officers were hurt.
At one stage a bullet was fired at police lines while burning vehicles were also pushed towards them.
A PSNI officer was also knocked unconscious as a barrage of stones, fireworks, blast bombs and other missiles were thrown at security forces.
Police say they used water cannon and fired 18 non lethal AEP (attenuating energy projectile) rounds at their attackers.
A total of three vehicles were hijacked during the trouble. The area was reported calm by 2am this morning.
There was also violence in Rasharkin, Co Antrim and in Armagh city, while security forces had to deal with hoax bomb alerts in Strabane, Co Tyrone, and in Lurgan, Co Armagh.
There were disturbances during the return leg of the Twelfth parade in Derry and violence in the Butcher's Gate area where one police officer sustained an injury.
Sinn Féin and the PSNI both blamed dissident republicans for orchestrating the violence.
Police assistant chief constable Alistair Finlay said: 'They displayed the worst possible face of Northern Ireland - a face of bigotry, sectarianism and intolerance.'
The PSNI said 200 young people were involved in the Belfast clashes but were directed by others.
'Police feel it was orchestrated by a few who clearly want to detract from the progress that was made,' Mr Finlay said.
'There were people working there together to create the right conditions to seek to attack police and portray Northern Ireland in a way that nobody else seems to want.'
The Taoiseach condemned the violence during an address to the Seanad this afternoon.
Brian Cowen said that the 'tiny and unrepresentative group' responsible for the riots in north Belfast, would not derail the peace process.
