The £15m bill for policing the Union flag protests is twice the amount spent by police on the entire marching season in the region last year, commanders have warned.
The spiralling financial implications of the public order policing were outlined by PSNI Chief Constable Matt Baggott and members of his command team as they briefed the Policing Board.
Loyalists have been holding demonstrations since early December when Belfast City Council voted to limit the number of days the flag flies over City Hall.
A number of the pickets have descended into serious rioting with almost 150 police officers injured in the disorder and nearly 200 people arrested. The youngest detained so far was 11 and the oldest 69.
"The past nine weeks have seen the Police Service of Northern Ireland hold the fragile line between peace and disorder in Northern Ireland," Mr Baggott said as he updated the board in Belfast at its first public meeting since the start of the year.
"This has come at a cost both physical and financial. A large number of officers have been injured and the cost is already above £15m."
The current running total for the policing operation stands at £15.6m. Responding to a board question on allegations about incidents of police incivility and brutality during the operation, the police chief assured members that he did not condone bad practice and urged anyone who had a grievance to complain. But he also insisted that officers had shown great bravery and restraint.
"I will say this for officers who have stood facing the abuse, having visited them personally in Antrim hospital, in the Royal, covered in paint and sand, (with) broken noses, to have seen the restraint that they have shown has been magnificent," he said.
Organisers of political marches are required to apply to the Parades Commission for permission to hold their event.
No such authority has been sought by those in the recent Belfast rallies.
While the commission is a controversial body, Mr Baggott yesterday urged Policing Board members to step away from the political debate around it and reaffirm the need for people to abide by its lawful determinations.