Loyalist paramilitaries have been blamed for rioting in north Belfast in which 40 police officers were injured.
Vehicles were set on fire during the trouble
Petrol bombs were thrown and a bus and 10 cars hijacked and set on fire in disturbances on the Crumlin Road.
The trouble followed the arrests of six men in connection with a loyalist feud, in which three men have been murdered.
Acting Assistant Chief Constable Wesley Wilson said he believed Thursday's riot was aimed at disrupting investigations into the feud between the LVF and UVF.
"I think this was an orchestrated attempt, because the police were in making arrests being pro-active - carrying out searches to try and stop this murderous feud that's ongoing," he said.
He said that while he did not have direct evidence he said that it was reasonable to expect that "loyalist paramilitaries such as the UVF" were behind the rioting.
Petrol bombs and a blast bomb were thrown and a bus and 10 cars were hijacked and set on fire in the trouble, which broke out shortly before 1730 BST.
It is understood that none of the injuries sustained by police are life-threatening. Officers fired 11 plastic baton rounds during the trouble.
Police in riot gear went to the scene
ACC Wilson said so many petrol bombs were thrown at police that they stopped counting.
He said that any allegations about police behaviour made about how police acted in the area would be investigated.
"I don't think there was heavy handedness," he said.
"The allegations that we have been made aware of are that in the face of provocation and unprovoked attacks on our officers while they're doing searches, eggs being thrown at them, one officer hit in the head with a brick, they say our officers were uncivil."
He said that no arrests were made at the time but that video evidence was being reviewed and he was confident police would identify rioters.
He said that attempts by community representatives to calm thing down had not worked, but appealed for them to continue in their efforts.
Northern Ireland's criminal justice minister David Hanson condemned the violence.
"Once again it is loyalist paramilitaries who have brought violence into loyalist areas," he said.
The funeral of Stephen Paul took place in north Belfast
DUP leader Ian Paisley said he was "shocked and appalled" at the scenes he witnessed in north Belfast on Thursday.
Speaking after discussing the riots with senior police officers on Friday, he said: "Those involved need to realise that it is their own community that they are harming by their actions.
"I would call upon those involved to step back and ensure that there are no repeats."
The area's SDLP assembly member, Alban Maginness, said there was no excuse for the riots or the viciousness of the hostility and violence directed at the police.
"We cannot have a situation where loyalist criminals organise and begin a riot just because the police move to hold them to account under the law," he said.
Meanwhile, the funeral of the latest victim of the loyalist feud has taken place in north Belfast.
Stephen Paul, 28, was shot dead as he sat in a car in Wheatfield Crescent last Saturday night.