Media playback is unsupported on your device Media caption Trouble erupted when a crowd that was blocking the road attacked a van

Police in Northern Ireland have said loyalist paramilitaries have organised some of the recent violence over flags.

In Belfast on Friday, eight officers were injured and 12 people arrested in clashes between loyalists and police.

Six officers were injured in the Crumlin Road and Ligoneill Road area of north Belfast and two at Shaftesbury Square in the city centre.

Senior officers have appealed to loyalists planning to protest in Belfast city centre later not to do so.

Loyalists opposed to new restrictions on flying the union flag at Belfast city hall have been holding protests across Northern Ireland all week after the city council voted to fly the union flag on designated days.

The city's Christmas Market will remain open on Saturday, with extra security in place, but politicians have warned that the economy is being damaged on what should be some of the year's busiest shopping days.

On Friday, US Secretary of State Hillary Clinton visited the city and condemned the violence.

Her comments came before Friday night clashes. Among those arrested on Friday was a boy aged 13.

Three people - two men, aged 18 and 29, and a 17-year-old boy - are due in court later on Saturday.

Police fear Saturday could bring more disruption or violence in Belfast, which is expected to be packed with Christmas shoppers.

Assistant Chief Constable Will Kerr, of the Police Service of Northern Ireland, said: "Police can now confirm loyalist paramilitaries are orchestrating some of the violence we have seen in the past 24 hours.

"We appeal to those who plan to come into the city centre to protest to stay away and let people get on with every day business such as Christmas shopping.

"Today I am urging everyone to be calm, take a step back and think about how this violence is affecting not just their own communities but the whole of Northern Ireland."

ACC Kerr said 27 police officers had been injured while dealing with disorder this week.

Ulster Unionist leader Mike Nesbitt also urged the protesters to stop.

"Anyone who attacks a police officer, anyone who riots, anyone who engages in illegal street protest, is disrespecting the values of the Union flag," he said.

"Stop now. You are losing the argument."

The SDLP's Conall McDevitt said: "The protesters are now damaging the economy of their own city.

"Last night's violence proved extremely damaging to both the footfall and the reputation of south Belfast's night-time economy, which in turn hurts local business owners and local jobs."

There were a number of developments during the disturbances on Friday evening:

Missiles were thrown at riot police and their vehicles in the Shaftsbury Square area of the city

Bricks and other missiles were also thrown at police on the O'Neill Road in Newtownabbey, on the outskirts of Belfast. Police said about 50 people were in the area

Water cannon was used in Belfast

There was trouble at the Mossley Mill civic centre in Newtownabbey, where 600 people were attending functions on the premises

Earlier, several small protests took place in Belfast, Bangor and Lisburn, as well as other areas of Northern Ireland

A protest at Alliance party headquarters near Holywood Arches in east Belfast caused traffic delays

Protesters blocked the road at University Street at the office of Alliance MLA Anna Lo

In other disturbances, about 200 people were at the DUP mayor of Newtownabbey's Christmas dinner and 400 were at a Christmas function involving singer Peter Corry.

About 30 to 40 loyalists who congregated at the gates hijacked and burned two cars and smashed the windscreens of other cars belonging to people attending the functions.

People at the play were delayed and those at the Christmas dinner had their evening cut short because entertainers could not get into the premises.

A situation arose where people inside could not leave and people attempting to enter were obstructed.

DUP assembly member Paul Girvan attempted to speak to the protesters but was initially stoned before being recognised by the loyalists.

He said that as far as he was concerned there was clear paramilitary orchestration.

"Irrespective of what anybody says there was definitely clear paramilitary involvement in this," he said.

"Some figures well known to myself were there and have links to the UVF (Ulster Volunteer Force)."

There have been protests since Monday when Belfast City Council voted to fly the union flag on designated days only.

Nationalists at Belfast City Council had wanted the union flag taken down altogether, but in the end voted on a compromise from the Alliance party that it would fly on designated days.

Unionists have said they consider the changes regarding the union flag to be an attack on their cultural identity.