Loyalists have attacked police with fireworks, stones and golf balls on a third night of trouble in east Belfast.
Officers fired three plastic bullets and used water cannon in an attempt to control a crowd of 100 loyalists who targeted police and set cars on fire.
Earlier, a 38-year-old man was held on suspicion of attempted murder after shots were reportedly fired at police.
During the day a protest took place over Belfast council's decision to stop flying the union flag every day.
Up to 1,000 loyalists demonstrated outside Belfast City Hall over the decision to fly the union flag only on designated occasions.
Police said they later dealt with public disorder in a number of locations including Templemore Avenue and the Albertbridge Road and advised people to avoid the area.
Bricks, bottles, fireworks and smoke canisters were thrown by the rioters on the Lower Newtownards Road.
The Police Service of Northern Ireland said it had fired three Attenuating Energy Projectile (AEP) rounds and deployed water cannon.
The AEP was introduced in Northern Ireland in 2005 and is designed to be safer than previous types of plastic bullet.
One officer has been injured but did not require hospital treatment and a number of arrests have been made.
The chairman of the Police Federation, Terry Spence, said he had no doubt that paramilitaries had been involved in the violence.
He said: "This is a very sinister development and quite clearly the police came under fire this afternoon from a gunman.
"What it clearly does demonstrate is that there has been paramilitary involvement in these attacks on police and it has been orchestrated, in the case of east Belfast, by the UVF (Ulster Volunteer Force)."
However, Democratic Unionist assembly member Robin Newton said it was too early to say whether the violence had been organised.
"I'm going to wait until the police actually indicate that from their intelligence, they haven't indicated that these riots have been orchestrated by the UVF," he said.
"We do need to be concerned about the number of injuries on the police officers - this is just not a good situation for the east of the city."
Three other men were arrested during the earlier trouble which happened close to the nationalist Short Strand area.
Some loyalists claimed it was sparked when they were attacked by republicans.
Police responded to the attacks on them by using water cannon.
It is the the third consecutive night that police have been attacked in Belfast.
Thirteen people appeared at a special sitting of Belfast Magistrates Court on Saturday night charged in connection with the recent rioting in east Belfast.
Eleven men and one woman were remanded in custody. One woman was released on bail.
The special two-hour sitting was before Judge George Connor.
Nine police officers were injured and 22 people arrested during rioting in east Belfast and Newtownabbey on Friday.
More than 30 petrol bombs and other missiles were thrown at police in east Belfast.
In Newtownabbey, police were attacked by a crowd throwing bricks and bottles.
A campaign of street demonstrations has been ongoing since Belfast City Council took a vote on 3 December which limited the number of days the union flag is flown at Belfast City Hall.