Fifteen people were arrested during another night of sporadic loyalist violence in Northern Ireland.
At least one police officer was injured while cross-community Alliance Party councillors were threatened when a small group disrupted a local council meeting near Belfast.
At one stage a crowd of 200 people confronted police in Belfast and bricks and other missiles were fired at flashpoints across the city.
There was also disorder in Carrickfergus, Co Antrim, and Portadown in Co Armagh.
About 80 protests were held across the province against Belfast City Council's decision to reduce the number of days the Union flag flies from city hall, police said.
The demonstrations left many Belfast retailers complaining of lost business, with main traffic routes blocked and the city centre relatively quiet days before Christmas.
Assistant Chief Constable Dave Jones of the Police Service of Northern Ireland said: "While most of the protests were peaceful, the violence witnessed in some areas is totally unacceptable.
"This is now the third week of protests and I am appealing to everyone involved to take a step back from this. It cannot and should not continue."
A meeting of Carrickfergus Council was disrupted but there were no injuries as around five protesters entered the building and threatened people inside, police said.
Politicians of most hues have called for the protests to end amid warnings of colossal damage to the local economy.