Loyalist violence over the flying of the union flag will be firmly dealt with for as long as necessary, Northern Ireland's police chief declared after a fourth night of rioting.

Matt Baggott's warning came just hours before fresh disturbances erupted in Belfast, with police once again coming under attack.

A mob hurled steel barriers, bricks, fireworks and bottles at officers patrolling Castlereagh Street in the east of the city on Sunday night. A protest in the area earlier in the day had dispersed, before factions broke away and launched an onslaught on police lines.

Disorder was also reported on Mountpottinger Road and Beersbridge Road, where a car was set ablaze. But PSNI chief constable Mr Baggott said officers were fully prepared to deal with the ongoing street disturbances.

"I want to commend the tireless courage of my officers at this very difficult time," he said. "Fifty-two colleagues have now been injured while protecting the community during a series of violent incidents. You may be assured there will be sufficient resources in the event of more disorder for however long is necessary."

So far, 70 people have been arrested in connection with the sporadic rioting over the flying of the union flag on Belfast's City Hall, and 47 charged. On Saturday, frontline officers reported coming under gunfire. Detectives from the Serious Crime branch later charged a 38-year-old man with possession of a firearm with intent to cause fear of violence, riotous behaviour and failing to remove a disguise when requested by a constable. He is due to appear at Belfast Magistrates Court later this morning, PSNI said.

More than 1,000 demonstrators had earlier marched on City Hall, and later around 100 loyalists hurled petrol bombs, fireworks, smoke canisters, bricks and other masonry at officers in the Newtownards Road area in the traditionally unionist east of the city. Police responded with water cannon and fired three plastic bullets. One officer was injured.

Politicians and church leaders held talks at the Rev Mervyn Gibson's Westbourne Presbyterian Church to try and forge a resolution. The meeting was attended by two unionist MLAs, the DUP's Robin Newton, the UUP's Michael Copeland, UUP leader Mike Nesbitt and other unionist councillors for the East Belfast.

Mr Gibson said unionist leaders were seeking meetings with police chiefs over allegations of brutality by some PSNI officers, including use of batons against non-rioters.

Robin Newton of the DUP said a lack of engagement from protest organisers was making it difficult to see an end to the unrest. "We have to find a way out of this, but how we do it I don't know," he said.