Northern Ireland Secretary Theresa Villiers has condemned the "scenes of disorder" outside Belfast City Hall which flared up earlier this week after a controversial vote on the flying of the Union flag.
Ms Villiers told MPs during Commons Northern Ireland questions that "there is nothing that could possibly justify" the violence, as she called for decisions on flag flying to be taken "on the basis of sound, reasoned discussions and democratic vote, not as a result of mobs seeking to beat down the door of City Hall".
Rioting loyalists injured 15 police officers, two council security guards and a press photographer when they tried to smash their way into Belfast City Hall.
On Tuesday, the Union flag was removed from City Hall for the first time in more than a century. The move brings the building into line with Stormont's Parliament Buildings where it is only flown on designated days.
Nationalists wanted to remove the Union flag permanently from Belfast City Hall. However, they voted in favour of a proposal from the non-sectarian Alliance Party that allowed it to be flown on 17 designated days throughout the year.
Ms Villiers said: "I fully appreciate the strength of feeling on the flying of flags, but there is nothing that could possibly justify the scenes of disorder that were witnessed outside City Hall in Belfast earlier this week. Yes, there are serious and significant sensitivities about flag flying, but these decisions must be taken on the basis of sound, reasoned discussions and democratic vote, not as a result of mobs seeking to beat down the door of City Hall."
Her comments came as Conservative Gareth Johnson (Dartford) said: "Northern Ireland is as much part of the United Kingdom as Dartford is, so does the Secretary of State share my deep disappointment that the Union flag will not fly continuously over Belfast City Hall and does she agree with the principle that no law should prevent the Union flag flying anywhere in the UK?"
Shadow Northern Ireland secretary Vernon Coaker condemned the violence on Monday evening, branding it "wrong, unacceptable and without justification".
Minister of State for Northern Ireland Mike Penning said: "What happened the other night was absolutely, fundamentally wrong. Police and security officers were assaulted and battered just doing their job.
"It is fundamentally wrong no matter what was said and done in the chamber in there. That was done in a democratic way - you might not necessarily like what happened, but it was done in a democratic way and it's fundamentally wrong what took place."