The violence erupting on the streets in Northern Ireland in recent days has been described by a police chief as the worst seen in years.
A bus was torched in west Belfast on Wednesday, while petrol bombs, fireworks and bits of masonry were hurled at police officers.
Over several hours of disorder, youths pelted petrol bombs and other missiles at each other from both sides of a peace wall.
A press photographer was also allegedly attacked.
Disorder has also taken place in Derry, Newtownabbey, Carrickfergus and Ballymena in recent days.
PSNI Assistant Chief Constable Jonathan Roberts told a press conference: “The scale of the disorder last night was at a scale that we have not seen in recent years in Belfast or further afield.”
Boris Johnson and Taoiseach Micheal Martin issued a joint call for calm after speaking over the phone on Thursday.
In a statement, the Irish Government said the two leaders stressed that violence was unacceptable.
“The way forward is through dialogue and working the institutions of the Good Friday Agreement,” the statement said.
“They agreed that the two governments would continue to stay in contact.”
The Stormont Assembly was recalled from the Easter recess for an emergency sitting on Thursday, where all parties condemned the violence.
Here we look at the complex reasons for the disorder and why it matters.
Changes to trade after the UK left the EU in January have played a role in exacerbating tensions in Northern Ireland.
Boris Johnson’s Brexit deal effectively created a border down the Irish Sea, as goods passing between Great Britain and Northern Ireland must be subject to checks.
A key part of the deal, known as the Northern Ireland Protocol, keeps Northern Ireland in the EU’s single market for goods, which the rest of the UK left on January 31.
The point of this idea was to prevent a land border between Northern Ireland and the Republic of Ireland, which remains in the EU.
Avoiding a land border is a key part of the Good Friday Agreement, the landmark peace deal which brought an end to most of the violence suffered during the Troubles.
However the plan to avoid inflaming tensions with infrastructure at the Irish border has instead seen anger shift to ports, where threats were made to staff and menacing graffiti emerged.
The reality of post-Brexit life – which has included some disruption to food supplies and online deliveries – has angered some in loyalist communities, over the perception that it has undermined Northern Ireland’s place in the UK.
A row over the decision not to prosecute 24 Sinn Fein politicians for attending a large funeral during the pandemic has also ratcheted up anger.
The funeral of former IRA leader Bobby Storey last June was attended by a number of senior republican politicians, including Deputy First Minister Michelle O’Neill.
Critics said the event broke coronavirus regulations, with large crowds appearing not to obey social distancing guidelines.
However prosecutors decided last month not to take action over the event, partly due to lack of clarity in the Covid-19 rules and partly due to interaction between the organisers and police ahead of the funeral.
The decision sparked outrage among some loyalist communities over perceived preferential treatment for the republican community.
Separately, months of living under strict lockdown rules may have also inflamed tensions.
There have been suggestions that paramilitary gangs have been stoking the violence in some areas, either directly or by encouraging young people to riot.
PSNI Assistant Chief Constable Jonathan Roberts said police were investigating whether there was any paramilitary involvement in the scenes in Belfast on Wednesday.
In Newtownabbey and Carrickfergus, the PSNI believes paramilitary involvement is partly to do with a rogue faction – the South East Antrim UDA – reacting to recent police operations targeting its criminal empire.
What are politicians saying?
In a joint statement, the five-party Executive said: “While our political positions are very different on many issues, we are all united in our support for law and order and we collectively state our support for policing and for the police officers who have been putting themselves in harm’s way to protect others.
“We, and our departments, will continue to work together to maximise the support we can give to communities and the PSNI to prevent further violence and unrest.”
On a visit to Northern Ireland on Thursday, NI Secretary Brandon Lewis welcomed the clear statement from political leaders and said he had urged everyone to “think very carefully” about the language used.
He admitted Brexit had caused issues, saying: “I’ll be the first to acknowledge over the first few months of the year there were real issues around how the protocol has landed for people, both as consumers and those in the loyalist and unionist community.
“The way to deal with these things is through a democratic and diplomatic, political process. There is no legitimisation of violence to deal with any of those issues.”
He also called on the Loyalist Community Council (LCC), which speaks for loyalist paramilitary groups, to be clear they oppose the violence.