Unionists have blasted Sinn Fein MP Francie Molloy for controversial remarks claiming that "Brits" were best at murdering.
The comment was made on Twitter on Wednesday as MPs debated whether to launch air strikes against IS in Syria.
It was in response to a tweet by Deputy First Minister Martin McGuinness urging against the military action.
Mr Molloy responded with the comment: "Brits back to what they do best, Murder."
DUP MP Gregory Campbell blasted the comment from the Mid Ulster MP as "grossly offensive".
"Mr Molloy appears to believe that the air strikes are what 'Brits do best', which is an interesting comment from a man who once threatened us that if the IRA didn't get its own way they would 'go back to what they do best'," he said.
"Francie Molloy could have gone to Westminster and voted against air strikes, just as Sinn Fein MPs could have turned up to vote on the welfare reform issue they caused so much difficulty over. To distract people from their impotence, it is much easier to issue an offensive tweet."
Ulster Unionist MP Danny Kinahan said Mr Molloy's tweet reveals a "deeper mindset within the psyche of some Sinn Fein members".
"They seem to have an irrational hatred of all things British - apart from pounds sterling, Westminster expenses and hospitality at Windsor Castle," he said.
TUV representative Richard Cairns added his outrage: "The comment by Francie Molly, Sinn Fein MP for Mid Ulster, were the lowest, most despicable and out of step comments anyone could have made. It is also deeply ironic that Molloy - who continues to justify and defend the IRA's bloody campaign in this province - should seek to brand anyone a murderer."
Sinn Fein has stood by Mr Molloy. West Belfast MLA Pat Sheehan said: "British military involvement around the globe does not have a distinguished history."