The DUP's Nigel Dodds has accused Sinn Fein of "wallowing in murder" over what he claimed was the party's "continued glorification of past terrorism".
The MP's remarks were made in response to the Deputy First Minister Martin McGuinness's stark warning to unionists who he said were "dancing to the tune of extremists" in their communities.
Mr Dodds's comments were made during yesterday's NI Question Time in the Commons and come a day after the five Executive party leaders met to discuss former US diplomat Dr Richard Haass's plans on Northern Ireland's most divisive issues.
The Haass talks continue to descend into a war of words after Mr Dodds went on to accuse Sinn Fein of causing "enormous damage to community relations".
He told the House of Commons: "The comments by Martin McGuinness on extremism are seen by many on both sides of the community as not only untrue, but a transparent attempt to distract from Sinn Fein's abject lack of leadership in relation to addressing their continued glorification of past terrorist crimes, as was witnessed in Castlederg this summer.
"Will the Secretary of State, urge Sinn Fein to stop wallowing in the filth of murder?"
Mr Dodds' party colleague Sammy Wilson stepped in to accuse the PSNI of "bias" in its treatment of loyalists.
He said: "While it is important that those who are involved in damaging public order disturbances should know they will be punished, the biased way in which the PSNI are dealing with these situations is alienating sections of the community and making effective policing more difficult."
Prime Minister David Cameron gave his backing to the Haass talks outcome, saying there was a "merit" in the proposals.
Mr Cameron said he hoped that the five main parties can take the Haass work forward with "all sides trying to agree".