Police car petrol-bombed near MP Naomi Long's office
The Ulster Unionist leader has called for an end to street protests after loyalists threw a petrol bomb into a car as a policewoman sat inside.
Police are treating the attack close to Alliance Party MP Naomi Long's east Belfast office as attempted murder.
The protests followed a vote by Belfast City Council to restrict the flying of the union flag at the city hall.
The NI secretary of state said those involved in the recent violence were "dishonouring and shaming the flag".
In the past week, as trouble flared across Northern Ireland, 29 police officers have been injured and 38 people arrested.
The latest and more serious incident took place on Monday at 19:35 GMT, when a gang of six men smashed the back window of the policewoman's car, which was parked on the Upper Newtownards Road, and threw in a petrol bomb.
The woman escaped unhurt.
Ulster Unionist leader Mike Nesbitt said on Tuesday that violence associated with protests could not be tolerated.
"It is anti-British to attack a police officer, it is anti-British to attack an elected representative," he said.
"Peaceful protest is fine but the chances of conducting protests without this kind of repercussion is so high that I have to ask people to give up their right."
Ms Long, the MP for East Belfast, received a death threat last week. A police car has been stationed outside her office since then.
Condemning Monday night's attack, Ms Long said: "There is no doubt in my mind that the car was targeted because it was undertaking patrols in the vicinity of my office and I find that absolutely repugnant."
Assistant Chief Constable George Hamilton said: "This was a planned attempt to kill a police officer which also put the lives of the public in danger and it is fortunate there were no injuries as a result of this attack.
"I am urgently appealing to those involved in ongoing protests to listen to their political leaders and step back from protest activity before someone is seriously injured or killed."
He said senior members of loyalist paramilitary groups working at local level were orchestrating violence but said that the leadership of those organisations may not be involved.
"Loyalism is very fragmented," he said.
"What you have is people at a local level in some ways disconnected from the senior leadership of those organisations actively involved in violence."
Ms Long said recent attacks on the Alliance Party bore "all the hallmarks of a pogrom".
Her party colleague, the North Down Alliance MLA Stephen Farry told the assembly on Tuesday there had been a second attempted arson attack on his constituency office in Bangor, County Down, on Monday evening.
Labour's shadow Northern Ireland secretary Vernon Coaker said the government needed to act.
There was also rioting in the loyalist Village area of south Belfast on Monday night.
Police were attacked with petrol bombs, bricks, masonry, bottles and fireworks, and attempts were made to put burning barricades across roads.
Police responded with water cannon.
At the Mountpottinger Road/Castlereagh Street junction in east Belfast, riot police separated rival crowds throwing missiles, although a small crowd of nationalist youths continued to stone police Land Rovers for a period.
Police are also investigating reports of an attack on a bar in Thomas Street, Armagh, which is owned by the husband of a Sinn Fein councillor.
It was reported that at about 21:00 GMT, windows in the bar were smashed and fireworks thrown inside. There were no reports of any injuries.
Publican Bernard Rafferty said a loyalist protest march had been passing the bar at the time of the attack.
"I was serving behind the bar and I noticed a crowd come by the window with union jacks - within 10 seconds I heard the windows starting to go in," he said.
"Next minute the door was bust open and there were large, what I thought at the time were pipe bombs, but they were large rockets fired into the bar."
At about 21:50 GMT, a car struck three men on the Newry Road in Armagh before being driven away. There was a loyalist protest in the area at the time.
The men's injuries are not thought to be life-threatening.
A 17-year-old boy was arrested a short time later in the Cavanacaw Road area, he has since been released on police bail pending further inquiries.
Alliance Party members and premises have been targeted since last Monday's vote on the city hall flag.
Alliance, Sinn Fein and SDLP councillors voted to limit the flying of the flag while the Democratic Unionist Party (DUP) and Ulster Unionists (UUP) opposed the move.
Rush-hour traffic was also disrupted in Belfast on Monday by a series of protests.
Some motorists moved less than a mile in the space of an hour.
Police maintained a presence at a number of locations in the city as roads were blocked by crowds carrying union flags and banners.
They said the biggest protest had been in Dundonald on Belfast's eastern outskirts, where about 500 people took part.
Monday was the eighth consecutive night on which loyalists have held demonstrations.
There have also been protests in towns such as Ballyclare, Limavady and Lisburn. But there was no violence.
First Minister and DUP leader Peter Robinson and Mr Nesbitt met on Monday night to discuss the flags issue.
In a statement they said they had "agreed to work on a joint basis with a view to urgently bringing forward political proposals to address widespread concerns across the community".
"The attempted murder of a police officer in east Belfast was a despicable act of terror," the first minister said.
"The masked men responsible do not act in the name of our union flag. They are bringing shame on it."
Meanwhile, Alliance Party leader David Ford has questioned whether the assembly commission should meet on Tuesday, given the "charged atmosphere".
A DUP proposal for a consultation on increasing the number of days the union flag is flown over Parliament Buildings at Stormont is due to be put forward by DUP MLA Peter Weir at the meeting of the assembly commission - the cross-party group that manages the estate.
The flag currently flies over the building for 15 days a year.
Mr Ford told the assembly that it was a time for measured reflection: "The question as to whether the assembly commission should meet in the charged atmosphere of today is one which is serious," he said.