Northern Ireland Secretary Theresa Villiers told the Commons that 32 police officers had been hurt and 38 people charged over the violence, which saw a policewoman flee her car after a petrol bomb was thrown into the vehicle.
The Northern Ireland Secretary said: "No-one can be in any doubt about this Government's support for the union and its flag, but those people engaged in the kind of violence we have seen in the past few days are not defending the Union flag.There is nothing remotely British about what they are doing; they are dishonouring and shaming the flag of our country with their lawless and violent activities. They discredit the cause they claim to support."
The "deplorable" outbreak of violence has seen an "appalling" death threat issued against Alliance MP Naomi Long, whose cross-community party backed the move to reduce the number of days the flag is flown from City Hall, said Mrs Villiers.
"There can be absolutely no excuse or justification for the kind of thuggishness and lawless behaviour; it is despicable, we condemn it unreservedly and it must stop immediately," she added. "The right of elected representatives to go about their daily business without the threat or fear of intimidation is one of the hallmarks of our democracy. These threats are nothing less than an attack on our democracy."
She urged all of Ulster's politicians to condemn the "disgraceful" violence and focus on other issues, including boosting the province's economy in the run-up to Christmas. Making a Commons statement, Mrs Villiers said: "Everybody has a responsibility to consider carefully the impact of their words and deeds on wider community relations. Once again, the trouble we have seen in Belfast and elsewhere underlines the urgent necessity of working towards a genuinely shared future for all the people of Northern Ireland."
Shadow Northern Ireland secretary Vernon Coaker said violence is never justified and is wrong. He said: "It cannot go on and Westminster's voice must also be heard. This violence would not be tolerated in London, Cardiff or Edinburgh and it shouldn't be tolerated in Belfast. A clear and strong message must be sent from this place today that says this violence is wrong, unacceptable and without justification."
Mr Coaker asked what discussions Ms Villiers had had with the Northern Ireland Justice Minister and the Chief Constable about resources and the continuing national security threat. He added: "I stand shoulder-to-shoulder with public representatives in Northern Ireland for democracy and against violence. When a Member of Parliament here is threatened and attacked I view it as a threat and an attack on all of us and everything that we stand for."
Ms Villiers said she had spoken three times to the Justice Minister since the events unfolded and three times to the Chief Constable. She said: "It does appear that some loyalist paramilitaries attended some of these events. There doesn't appear to be evidence of organised orchestration by paramilitary groups, but I'm sure this is something the PSNI will be reviewing carefully and continue to investigate as part of their wider investigation."