A policeman narrowly escaped with his life after a loyalist gang of 15 masked men threw a petrol bomb into his unmarked car.
The attack happened on the Newtownards Road in east Belfast at around 7.30pm on Monday night as protests and violence over the Union flag row continued.
The gang smashed the windows of the police vehicle and then threw the firebomb while the officer was still inside.
Police are treating the petrol bomb attack as attempted murder.
A paint bomb was hurled at another unmarked police vehicle.
Both were guarding Alliance MP Naomi Long’s constituency office when they were attacked.
The MP, who is under a loyalist death threat after her party voted to only fly the flag on designated days, said the petrol bombing was “an obscenity”.
She said: “There was an officer inside who managed to get out and was lucky to escape with his life. This is attempted murder and I unreservedly condemn it.
“It is an obscenity that an officer simply doing his job was attacked in this way.
“There is no place in society for this kind of violence and no place in Northern Ireland for this type of violence as we try to move forward.
“It is time for real leadership to be shown to put an end to this before somebody loses their life.”
PSNI Chief Constable Matt Baggott said he was very angry about the attack and that significant resources would continue to be deployed to tackle the violence.
“I think we have been very fortunate that no one has been killed or seriously injured this evening,” he said. “There is still an opportunity for people to take a step back and reflect on their actions, because what we’re seeing at the moment is simply mob rule.
“It is sporadic violence but it is very intense.
“We have again an assault on democracy. We have courageous police officers being attacked. We’re making many arrests as we speak and that will continue.
“But there has to be a collective voice to bring this to an end.”
Alliance leader David Ford said: “This attack served no purpose and must be condemned by all.
“This was an attempt to kill police officers. This violence must end now. While I respect the right to peaceful protest, it is clear that there is a need for these protests to end due to the violence and increased tensions on the streets.”
He said he wanted the Government to do more and take the threat to democracy seriously.
UUP leader Mike Nesbitt asked protesters: “What is British about attacking a police officer... and what is British about blocking the entrance to an acute hospital?”
DUP minister Edwin Poots said those involved in violence were attacking democracy, but he defended peaceful protesters.
He called on people angry about the flag decision not to engage in violence and not to block roads.
East Belfast UUP councillor Jim Rodgers said: “I totally and utterly condemn what’s happened and appeal to those involved to please stop this madness now before someone loses their life.
“I’m as angry as the next person over the Union flag business at City Hall, but we can protest in a dignified fashion.
“Those who have got any influence over these people, I would ask them to influence them to stop this violence now.
“I was brought up in this area. I’m not going to stand by and allow people to destroy it.”
The Police Federation which represents rank-and-file officers said: “These barbaric attempted murders will only strengthen our resolve to protect the community.”
People in the area also condemned the attack on the police.
A man who lives in the housing estate near Mrs Long's constituency office said: “There is no call for it. Many pensioners live in this area and a woman in that house there has just had a triple bypass — this is the last thing we need.
“I can understand people's frustrations but this violence needs to stop before somebody is killed.
“I know Naomi personally and she is a lovely woman, it is terrible the way she is being treated,” the man added.
But not everyone felt the same.
One man said he agreed with whoever attacked the vehicles, adding: “It should have been Naomi Long's office that got it.”
Labour Northern Ireland spokesman Vernon Coaker called on Secretary of State Theresa Villiers to make an urgent statement.
He said: “Loyalist paramilitaries have been involved in orchestrating sustained rioting and tonight a group of masked men tried to murder police officers by throwing a petrol bomb into a police car.
“A clear and strong political response at Westminster is needed.”