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Union flag protests: Twenty-nine officers hurt in Belfast
The BBC's Chris Page: "This dispute is proving very difficult to resolve"
Twenty-nine police officers have been injured in rioting in Belfast following a loyalist protest over the union flag.
Officers fired six baton rounds and used water cannon during the 40th day of street protests.
The latest unrest began around 14:30 GMT, when loyalists and nationalists clashed at a sectarian interface at Short Strand, east of the city.
PSNI Chief Constable Matt Baggott said officers had used "exceptional courage" to bring the situation under control.
Demonstrators were passing the nationalist Short Strand area - after a 1,000-strong protest outside Belfast City Hall against the council's decision to restrict the flying of the Union flag - when the violence broke out.
Bricks, stones and missiles were thrown at police and four officers were taken to hospital with injuries - two were later discharged.
A car was later set on fire at the junction of Castlereagh Street and Templemore Avenue.
The violence subsided in the early evening but after 21:00 GMT it erupted as loyalists attacked police again at Castlereagh Street. Police used water cannon on rioters to push them away from the interface with the Short Strand.
A car was set on fire at Castlereagh Street, east Belfast
Chief Constable Matt Baggott said: "This was a difficult operation dealing with a large number of people determined to cause disorder and violence.
"My colleagues brought the situation under control with exceptional courage and professionalism. I know the vast majority of people will be grateful for their efforts.
"Police will continue to engage with all those committed to finding a solution to these issues."
Loyalist street demonstrations have been taking place for almost six weeks, since Belfast City Council voted to change its longstanding union flag policy on 3 December.
The council, which now has a nationalist majority, voted to fly the flag at Belfast City Hall on a number of designated days, rather than every day of the year.
The majority of the street demonstrations have passed without incident, but some have resulted in serious rioting.
On Friday night, four police officers were injured during union flag protests, one was taken to hospital.
The most serious violence took place outside Belfast - in Newtownabbey and Carrickfergus in County Antrim. Officers fired five plastic bullets as rioters threw more than 30 petrol bombs.
In Rathcoole in Newtownabbey, a distressed pensioner confronted protesters whom he blamed for the closure of a nursing facility where his terminally ill wife was being cared for.
The elderly man was jeered at when he called the protestors actions a 'disgrace'.
The chairman of one of the groups behind the flag protests said he could not support people being stopped from getting to hospitals, but that disruption was inevitable.
Dozens of police officers have been injured during the 40 days of protests and more than 100 people have been arrested.
Angry residentsAlliance MLA Judith Cochrane condemned the violence.
"This violence cannot continue. People want to go about their daily lives, but are really angry at the disruption they have faced in recent weeks," she said.
"These protests and violence are doing untold damage to traders and businesses and Northern Ireland's image is being tarnished. What we need to do is to show the rest of the world that Northern Ireland is open for business, otherwise potential investors will take their jobs elsewhere."
SDLP MLA Conall McDevitt said: "This is a craven attempt at the most vicious, barbaric mob rule undertaken by those with no motivation except the destruction of any progress towards a truly shared society."
Ulster Unionist leader Mike Nesbitt said it had been a "bad 24 hours for the image of unionism".
Northern Ireland First Minister Peter Robinson says the political process is "the only way forward"
"Images of burning vehicles, petrol bombs being thrown at the police, and people who carry the union flag but mask their faces have nothing to do with my vision of being British," he said.
"Street violence from so-called unionists, no matter what age, advances nothing but the cause of Irish nationalism. It is high time those involved in rioting realised they are destroying the very cause they hope to promote."
Sinn Fein leader Gerry Adams has called for an "all-party, cross-community response to the protests and violence".
"After the Massereene attack in 2009 in which two British soldiers were killed, Martin McGuinness and Peter Robinson brought together all of the political leaders, church and civic leaders to map out a way forward and to ensure that the tiny minority of voices who want to undermine the progress that has been made do not succeed," he said.
"That approach is needed again. The Unionist Forum established by the DUP and UUP may have a role to play but it is limited. Stability and inclusivity and progress are not in the gift of one section of people. Everyone has to be involved."
Mr Adams said the "tiny minorities" who want to cling to the past must be rejected.
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