* Police body says period most challenging in last decade
* Analysts say lack of numbers limits risks to peace process
* Rioting enters fourth night as number arrested rises to 70
Pro-British militant groups are instigating riots that have rocked the Northern Irish capital Belfast in the past month, a police officers' representative said on Sunday as officers came under attack again.
The violence stems from protests over the removal of the British flag over Belfast City Hall. It has been among the province's worst since a 1998 peace accord ended 30 years of conflict in which Catholic nationalists seeking union with Ireland fought British forces and mainly Protestant loyalists.
Fireworks, bottles and bricks were flung at officers for a fourth successive night on Sunday although a police spokeswoman said the trouble was not on the scale of the previous night, when police came under attack with petrol bombs and gunfire.
By Sunday, 70 people had been arrested, including a 38-year-old man detained on Saturday on suspicion of attempted murder over the shooting.
Police had said that members of pro-British militant groups helped to orchestrate and had taken part in the first wave of violence in early December. The Police Federation for Northern Ireland (PFNI) said the recent attacks showed this was now clearly the case.
"What it quite clearly demonstrates is the fact that paramilitaries have hijacked this flags protest issue and they have now turned their guns on the police," federation chairman Terry Spence told BBC radio.
"It is very clear that there are leading members of the UVF (Ulster Volunteer Force) who are exploiting this and are organising and orchestrating this violence against police officers who are out there trying to uphold the law and prevent anarchy on our streets."
Both the UVF and Northern Ireland's other main loyalist militant group, the Ulster Freedom Fighters, ceased hostilities in 2007 and decommissioned their stocks of weapons following the signing of the peace deal.
At least 3,600 people were killed in the 30 years of violence before the 1998 peace deal.
In scenes that recalled that earlier strife, pro-British loyalists began rioting in early December after a vote by mostly nationalist pro-Irish councillors to end the century-old tradition of flying Britain's Union flag from the city hall.
"NO STOMACH FOR THIS"
Analysts said that, although the violence was worrying, the small numbers of protesters indicated they might be unable to develop any strength.
"Clearly the violence is a step up in terms of what's happened more recently but they're simply not getting people out on the street," said Peter Shirlow, a professor at Queen's University who has spoken with protesters in recent days.
"Protestants are annoyed about the flag but they're even more annoyed about the violence. There's no stomach for this, that mass mobilisation is just not there anymore."
The police federation's Spence said, however, that it was the most challenging time for police in a decade. Church leaders and community workers held talks behind the scenes on Sunday to try to quell the violence.
Militant Irish nationalists, responsible for the killings of three police officers and two soldiers since an increase in tensions from 2009, have also not reacted violently to the flag protests, limiting any threat to the 15 years of peace.
The British-controlled province's first minister, Peter Robinson, said on Friday that rioters were playing into the hands of nationalist groups who would seek to exploit every opportunity "to further their terror aims".
The moderate nationalist Social Democratic and Labour Party (SDLP) party said on Sunday that shots had been fired using a ball-bearing gun at the house of one its councillors in Belfast, shattering windows.