There have been further clashes between police and loyalist protesters in east Belfast, with reports of shots being fired and a 38-year-old man being arrested on suspicion of attempted murder.
The violence, which flared for the third night in a row, is linked to last month's decision by councillors to limit the number of days the union flag is flown over Belfast City Hall.
Police, dealing with disorder in Newtownards Road, Albert Bridge Road, Castlereagh Street and Templemore Avenue, fired three plastic baton rounds and also deployed water cannon.
The trouble overnight saw police officers attacked with fireworks, stones, bricks and other missiles. Several cars were also set on fire.
The PSNI said one officer was injured and a number of arrests were made.
Last night, 13 people appeared before a special sitting of Belfast Magistrates Court, charged in connection with public order offences.
A woman was released on bail and 12 people were remanded in custody.
Tánaiste Eamon Gilmore yesterday condemned the recent violence.
He said the attacks were not the mark of legitimate protest but the actions of a small group who want to bring Northern Ireland back to a darker past.
Northern Ireland First Minister Peter Robinson said violence against the police was a "disgrace" and those behind days of unrest were playing into the hands of dissident republicans.
Mr Robinson said: "The violence and destruction visited on the PSNI is a disgrace, criminally wrong and cannot be justified."
Loyalist activist Willie Frazer said the police should have had more of a presence on the areas where most of the violence took place.
Mr Frazer said he is organising a demonstration in Dublin next weekend as part of the ongoing protests over the flag controversy.
Mr Frazer, who is based in Markethill, Co Armagh, said he expects 150 people to take part in a short protest at Leinster House at midday on Saturday, 12 January.
