The move came after another night of violence in the Province, which included a gang of 15 men throwing a petrol bomb into the unmarked vehicle of a police officer after surrounding and smashing it.
The attack happened outside the Belfast offices of Alliance Party MP Naomi Long.
Ms Long's party has been blamed by Loyalists for supporting the Nationalist SDLP and Sinn Fein in pushing through the vote to lower the flag.
Police are treating the attack by Loyalists on the officer as attempted murder.
Assistant Chief Constable George Hamilton, of the Police Service Northern Ireland, said the officer was lucky to escape with his life.
He said: "This was a planned attempt to kill a police officer that also put the lives of the public in danger and it is fortunate there were no injuries."
It was the worst incident in another night of sporadic violence in parts of the city involving Loyalists who took to the streets in protest against a decision by Belfast City Council to fly the Union flag only on designated days.
Officers were also attacked with petrol bombs in south Belfast close to the M1.
More talks were taking place today between Peter Robinson, Northern Ireland First Minister and leader of the Democratic Unionist Party, and Mike Nesbitt, leader of the Ulster Unionist Party, to try to agree some sort of political strategy to ease tensions and end the violence.
It follows a meeting between the pair in Belfast yesterday. They have been heavily criticised by Nationalist representatives over their leadership since the trouble flared a week ago.
Mr Robinson and Mr Nesbitt have already called for Loyalist restraint and say they have agreed to work on a "joint basis with a view to urgently bringing forward political proposals to address widespread concerns across the community".
There were also protests in Limavady, County Londonderry, Ballyclare, County Antrim, Ballycastle, County Antrim, and Cookstown, County Tyrone, where the car of a DUP member of the Northern Ireland Assembly, Ian McCrea, was surrounded by angry Loyalists.
Several roads in Belfast were blocked and at one stage police were also attacked with petrol bombs and fireworks at Broadway, not far from the M1.
Meanwhile in Armagh city, Sinn Fein accused masked Loyalists of attacking a bar after staging an impromptu march with no police presence.
They claimed windows were smashed and fireworks thrown.
PSNI Chief Constable Matt Baggott said that some of the violence was intense and there was clearly some paramilitary involvement.