Loyalists have been urged to cancel more planned street demonstrations over a Belfast City Hall decision to restrict the flying of the Union flag.
Amid fear of further violence following attacks on offices of the cross-community Alliance Party, Northern Ireland First Minister Peter Robinson called on protesters to suspend their action. US Secretary of State Hillary Clinton is due to visit Northern Ireland on Friday and is expected to endorse appeals for calm.
There were threats to hold another mass demonstration in Belfast city centre on Saturday, one of the busiest shopping days of the year, when many people could be at risk if violence breaks out, police said.
Police Service of Northern Ireland (PSNI) assistant chief constable Will Kerr warned: "To encourage thousands of people to come to Belfast city centre on one of the busiest days of the year would be madness."
Mr Robinson said the action should be abandoned. "Britishness will not be progressed by acts of violence. Anyone engaging in wanton violence or intimidation does not defend our national flag but disgraces it," he added.
Anti-sectarian Alliance members of the regional assembly at Stormont and Westminster have been targeted at their homes and offices by arsonists, vandals and pickets. It follows the party's pivotal backing for a reduction in the number of days which the flag can be flown from the city hall each year.
Trouble flared on Monday night after a protest outside the council meeting which ratified the decision, championed by some nationalists but bitterly opposed by many unionists, turned ugly. Golf balls, bottles and crush fencing were thrown at police officers.
On Wednesday night, unrest spread to a small number of other areas in Northern Ireland. In Carrickfergus, Co Antrim, more than 1,000 rioters burned down the office of Alliance MLA Stewart Dickson and four police officers were injured as non-lethal rounds were fired to dispel protesters.
In the seaside town of Bangor, Co Down, arsonists attempted to set light to the office of Stormont Employment and Learning Minister Stephen Farry but were thwarted by a passing police patrol. In the same town, a window was smashed at the home of two Alliance councillors with a 17-month old baby.
Chief Constable Matt Baggott said people were acting without thinking because of anger. "That anger leads to problems, which leads to people losing their lives," he said.