The PSNI has said there is "no doubt" there is a loyalist paramilitary link to violence in Belfast in recent days.
Trouble erupted in the Sandy Row area of south Belfast last night for the second time in 72 hours.
The area, close to the city centre, is one where the Ulster Defence Association has a strong presence and influence.
More than 300 police officers in riot gear and a large number of armoured Land Rovers were deployed in the area last night.
A small crowd of rioters - most of them teenagers - attacked police with petrol bombs, chunks of masonry and other items.
They also again attacked a shop owned by a Syrian family that was virtually destroyed when set on fire on Saturday night following an anti immigration rally in the city centre.
The shop, which is on the ground floor of a building with residential apartments on the upper floors, was set alight again, but the flames were extinguished by police officers.
A man in his 50s was seriously injured in a racially motivated assault, which is being treated as a hate crime.
Police said witnesses reported seeing attackers stamp on his head, while members of the public tried to shield him.
The PSNI has confirmed that two plastic bullets were fired during the disorder, with a rioter hit on the hand.
A 15-year-old boy was arrested on suspicion of riotous behaviour and remains in police custody.
Speaking at a press conference at PSNI headquarters this afternoon, Temporary Assistant Chief Constable Melanie Jones was asked if the use of plastic bullets was justified, given the age profile and relatively small number of rioters.
"The justification is always based upon the assessment at the time in terms of the risk to the officers, the risk to the wider community, the risk to properties," she said.
"It is a high end tactic, it was carefully considered by the police commanders on the ground last night. I am confident that it was the right tactic to use.
"We are always cognisant of children who may be at the scene and that is always a consideration when we are deciding whether or not it is an appropriate tactic."
The senior officer also said there was a degree of orchestration and organisation of last night's violence.
"I have no doubt there is a paramilitary element to this, but I am not in a position to say that it is this that is the main organiser or orchestrator of these events.
"However, we do keep an open mind to this and this will be part of our investigative strategy."
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'A dynamic and difficult scenario'
Assistant Chief Constable Melanie Jones said the unrest in Belfast last night and on Saturday night was "a really dynamic and difficult scenario" with police coming under "sustained attack."
She described those involved in the violence as "despicable people who are intent on violence".
However, ACC Jones said what occurred last night was different to what happened at the weekend in Belfast.
"On Saturday, we saw mainly older, adult people who became involved in disorder," she said.
"Last night it was clear to us that there was a younger element, teenagers mainly, who were involved in the disorder, but there was an element of organisation and orchestration from what appeared to be older adults present at the scene."
Ms Jones said at this stage, the PSNI has an open mind as to who is "orchestrating and organising" the violent protests.
Asked for her message to people who are feel to frightened to leave their homes, ACC Jones insisted the PSNI has "an appropriate policing deployment" and "plenty of visibility".
"We are seeking to reassure the public, we will have appropriate policing resources available throughout the forthcoming days."
She the Police Service of Northern Ireland are actively pursuing and identifying offenders and making arrests.
"We are working with minority and community groups to give them specific and tailored support."
"I would reiterate that generally speaking, this is one of the safest communities to live in in the United Kingdom," she added.
The senior PSNI officer also said the police are working with An Garda Síochána to establish if people who had travelled from the Republic to take participate in the protests had committed any offences.
"We were aware on Saturday of the potential for people to have travelled from Dublin and the South into Belfast to take part in protest and or disorder."
"That is part of the investigation that's ongoing to identify if any of those people committed offences, who they are and to bring them to justice through our joint cooperative working arrangement," she added.
The PSNI have also urged anyone with information about the incidents to contact the police.
In a public appeal, ACC Melanie Jones said: "If you know who is involved in this disorder in your community, please report it either through Crime Stoppers or provide information or footage through the major incident portal."
"These people have no place in our society and I am asking for communities to stand up and say that openly, and make sure there is no place to operate for people who bring such harm on our communities."
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