Petrol bombs, fireworks and masonry were thrown at police on Thursday during a second consecutive night of violence in Belfast despite calls for calm from leaders in Stormont, London, Dublin and Washington.
A water cannon was deployed on rioters on the Springfield Road as groups gathered on either side of an interface between loyalist and republican areas of west Belfast, near to where trouble erupted on Wednesday evening.
It followed more than a week of unrest and disorder across other parts of Northern Ireland, including in Newtownabbey, Carrickfergus, Ballymena and Derry.
But what is fuelling the violence, who is behind it, and what are Northern Ireland's political leaders and police service doing about the disorder?
Brexit’s Northern Ireland protocol
Loyalists are angry at Northern Ireland's new trading arrangements, which were implemented because of Brexit, under a mechanism known as the protocol.
Because Northern Ireland stayed in the EU's single market after Brexit, customs checks are required on goods entering Northern Ireland from the rest of the UK.
This effectively created a border down the Irish Sea and was done to avoid constructing a land border on the island of Ireland – a key element of the Good Friday peace deal, which brought an end to decades of violence between loyalist and republican paramilitaries.
The trading arrangements have caused some disruption to trading in food supplies, plants and online deliveries. But perhaps more importantly loyalists – who want to remain part of the UK – believe that the new rules cut Northern Ireland adrift from the rest of Britain and therefore threaten their British identity.
This view is shared by Northern Ireland's unionist parties, including the governing Democratic Unionist Party, which supported Brexit but is now campaigning to have the protocol scrapped.
Northern Ireland's cross-community party Alliance, and nationalist parties including Sinn Fein – who want Northern Ireland to be reunited with the Republic of Ireland – say the issues with the protocol are teething problems and that unionist parties are not working to find practical solutions to the problems.
They have also challenged unionist parties to present a credible alternative to the protocol.
Surge in sinister behaviour
Since the end of the Brexit transition period in January, there has been growing discontent within the loyalist community over the Irish Sea border.
Graffiti has appeared on walls at Northern Ireland ports describing staff working there as "targets", while PSNI assistant chief constable Mark McEwan warned, "we are picking up social media sentiment of a growing discontent, particularly within the Protestant/loyalist/unionist community."
Mr McEwan added that the discontent "has not manifested itself in any outworkings at this point". Amid a surge in unionist political activity to have the protocol scrapped that reality has now changed, as evidenced by the events in Belfast, Derry, Newtownabbey and Carrickfergus over Easter weekend.
Funeral of ex-IRA man Bobby Storey
In addition to concerns over the Northern Ireland protocol, some loyalists have accused the PSNI of "two-tier policing". They argue the PSNI is treating the nationalist community differently from the loyalist community.
These fears were exacerbated last week when the Public Prosecution Service decided not to prosecute Sinn Fein politicians for attending the funeral of Bobby Storey, a senior Republican figure who is said to have been the head of the IRA's intelligence unit in the 1990s.
Deputy first minister and Sinn Fein vice-president Michelle O'Neill was among 2,000 mourners to attend the funeral last June, at a time when the loyalist marching season would soon be getting underway in a normal year. Storey's funeral was held while lockdown restrictions prevented mass gatherings, sparking a political row. First minister and DUP leader Arlene Foster is calling for PSNI chief constable Simon Byrne to resign over how police handled the funeral.
The PSNI denies accusations of so-called two-tier policing and says its handling of Storey’s funeral was appropriate.
Analysts say a combination of unrest over the protocol and anger at the funeral lit the fuse that sparked violence over the weekend. The recent arrests of senior members of the Ulster Defence Association, a loyalist paramilitary group, may have contributed to the violence in the Newtownabbey area, police say.
Who is carrying out the violence?
PSNI Chief Superintendent Davy Beck said the attacks in recent days have been "clearly orchestrated" by criminal elements.
He refused to be drawn on reports that the South East Antrim UDA are behind the violence, saying only: "As I said, I believe that this is a group of disaffected criminal gangs and we will investigate that.
"We will review all our footage. We will review all the information coming in, in terms of who has been involved."
According to the Belfast Telegraph, members of the illegal group warned business owners in Newtownabbey to pull down their shutters early to protect themselves against a weekend of planned riots. The police were reportedly notified.
The UDA is among a number of illegal groups represented politically by the Loyalist Communities Council (LCC). On 3 March the LCC announced that loyalist paramilitaries were temporarily withdrawing their support for the Good Friday peace deal.
What are the political parties saying about the violence?
Northern Ireland secretary Brandon Lewis said the scenes were "completely unacceptable", adding "violence is never the answer".
Ms Foster condemned the violence in Belfast and urged young people not to get involved in criminality.
“I know that many of our young people are hugely frustrated by the events of this last week but causing injury to police officers will not make things better," she said.
“I appeal to our young people not to get drawn into disorder which will lead to them having criminal convictions and blighting their own lives."
She added: “I also ask parents to play their part and be proactive in protecting their young adults.”
Sinn Fein claimed the "reckless rhetoric" of the DUP and other unionist parties had caused violence.
South Belfast MLA and communities minister Deirdre Hargey said: "They have fed young people with misinformation and lies that their identity is under threat when it isn't."
Alliance Party leader and justice minister Naomi Long called for an end to the disorder, warning it would end in tragedy.
“The violence has to stop, but so does the political cover given through vague comments and empty threats," she said.
"There is no room for ambiguity – this violence must be condemned by a united Assembly, which fully supports the rule of law in Northern Ireland. Anything less is just allowing a culture of lawlessness to grow and further poison our community.”
The Ulster Unionist Party MLA Doug Beattie branded the violence "disgraceful", saying "right-minded people must condemn where we see kids being goaded onto the streets by adults."
One of those involved in the rioting over the weekend was reportedly 12 years old.
Mr Beattie added: "Where we have criminal drug gangs organising rioting in other parts of the country – it is utterly disgraceful.
"Let's not tar everybody here with a very small minority but that small minority is certainly capturing the headlines and all for the wrong reasons."
"I have long had an issue with these people [South East Antrim UDA] and they have to be called out time and time again."