Britain's Northern Ireland Secretary, Theresa Villiers, has described the recent trouble in Belfast as "simply incomprehensible".
Ms Villiers suggested that the best way to resolve it is through dialogue.
Three police officers were injured during clashes with protesters last night and eight people have been arrested.
There is anger at the decision to restrict the flying of the British union flag at Belfast City Hall, but Ms Villiers said the violence is counter productive.
Police fired baton rounds and deployed water cannon on rioters in east Belfast last night.
The fifth successive night of trouble in the area came after hundreds of loyalists staged a largely peaceful protest at Belfast City Hall.
The disorder erupted as around 250 demonstrators from east Belfast returned from the city centre past a volatile community interface at the republican Short Strand.
Police said a number of missiles were thrown at the protesters from the Short Strand area, where around 70 youths had gathered.
The trouble soon spiralled from there as police moved up the adjacent Newtownards Road to separate rival factions.
Officers were attacked with petrol bombs, paint bombs, fireworks and heavy masonry while rioters damaged vehicles with hatchets and sledge hammers.
Protesters constructed a barricade in the middle of the road and set it on fire.
Police also received reports of an attempted car hi-jacking in the nearby Templemore Avenue area and attempted lorry hi-jacking in the Albertbridge Road area.
Police deployed water cannon and five baton rounds were fired. Calm was restored around 10pm.
The earlier demonstration at Belfast City Hall came as the council met for the first time since its controversial decision to limit the flying of the flag on the roof.
Loyalist protests have been continuing across the North since early December in response to the vote by Belfast councillors to only fly the flag above City Hall on designated days instead of all year round.
The first of these days is this Wednesday, when the flag will be raised to mark the birthday of the Duchess of Cambridge.
More than 60 police officers have been injured in flag-related unrest in the last five weeks, with around 100 people arrested.
Two males and two females were arrested in east Belfast last night for riot and public order offences.
Earlier Northern Ireland Chief Constable Matt Baggott claimed senior members of the paramilitary Ulster Volunteer Force (UVF) had been orchestrating the street violence in east Belfast.
Mr Baggott said there was no evidence that the organisation’s leadership endorsed their actions.
Police also reported some disorder elsewhere in east Belfast, in the Dundonald area.
Last month, Sinn Féin, the Social Democratic and Labour Party (SDLP) and the cross-community Alliance Party all voted to limit the number of days the flag flies at City Hall, with all unionist members of the council opposing the move.
Since then, elected representatives from all sides and some representing areas beyond Belfast have received death threats. The latest was against SDLP Assembly member for Mid Ulster Patsy McGlone.
A parcel containing a sympathy card referring to Mr McGlone and a bullet was intercepted at a postal sorting office.
The flag issue was not on the formal agenda of last night’s Belfast City Council meeting, but councillors did spend an hour debating the matter.
At the outset, DUP lord mayor Gavin Robinson urged members to show moderation in the discussion.
While some angry words were exchanged between councillors on opposing nationalist and unionist benches, the debate was generally even-tempered and well ordered.
Sinn Féin’s Jim McVeigh accused unionist politicians of failed leadership and said they had allowed themselves to be “led by the nose” by a small band of extremists.
He said councillors would not be bowed by threats from loyalists.
“We won’t be intimidated by those threats,” he said.
“Their protests are pointless and they will have absolutely no impact on decisions that we take.”
He said his party would respect British tradition but told unionists that respect was “not one way”.
But his claims were met with a vociferous response from unionists.
Democratic Unionist councillor for east Belfast Robin Newton accused Mr McVeigh and Sinn Fein of “bulldozing” the flag vote through council.
“It was purely a political decision, a pure political decision,” he said, rejecting the claims that unionists had not shown leadership.
But Mr Newton also called on loyalists engaged in the protests to seek a political route to voice their grievances instead.
“All sections of the unionist community should involve themselves in politics in Northern Ireland,” he said.