The leaders were gathered at a Presbyterian church in Belfast, Britain's Channel 4 News reported. Robin Newton of the Democratic Unionist Party said efforts to negotiate a resolution were hampered by a lack of participation by protest organizers.
"We have to find a way out of this, but how we do it I don't know," he said.
"I think we need a bit of calm and reflection. We need to get wise heads together."
Along with dealing with ongoing demonstrations, police were investigating a shooting attack on the home of a nationalist councilor, Claire Hanna, in south Belfast, the TV station said. Hanna and her husband and their infant daughter were not home at the time.
The protests began in December after the Belfast City Council voted to reduce the number of days the union flag can be flown at City Hall. The rallies escalated to violence this past week, leading to the arrest of several people, including a 38-year-old man suspected of firing shots at police Saturday.
Terry Spence, chairman of the Police Federation for Northern Ireland, said the shootings raised the stakes.
"What it quite clearly demonstrates is the fact that paramilitaries have hijacked this flags protest issue and they have turned now their guns on the police," Spence said.
"There is no doubt that it has been exploited by the paramilitary grouping known as the Ulster Volunteer Force, and it is very clear that there are members of the UVF, leading members of the UVF, who are exploiting this and are organizing and orchestrating this violence against police officers who are out there trying to uphold the law and prevent anarchy on our streets."
Police Superintendent Paula Hillman told the BBC officers were subjected to "sustained, serious, violence" in Saturday's confrontations that involved up to 1,000 loyalist protesters.
"They are being attacked with petrol [gasoline] bombs, masonry and bricks," she said.
"Lasers are also being used against police officers and those in the police helicopter.
"We're sending out a very clear message to people -- we respect people's rights to peaceful protest but if you are going to engage in violence, we will robustly apprehend those either by arresting them at the time or as a result of subsequent follow-up investigations and bring those people before the courts."
Since Thursday, 19 officers have been injured and 27 people arrested, bringing the total since the Dec. 3 flag vote to 52 officers injured and 70 people arrested, the BBC said.