DUP MP Nigel Dodds has accused Sinn Fein of "wallowing in murder" after Deputy First Minister Martin McGuinness claimed unionists had pandered to loyalist extremists during the Haass talks.
During Northern Ireland question time yesterday, Mr Dodds told the House of Commons that Mr McGuinness's remarks were an attempt to detract from Sinn Fein's "continued glorification of past terrorism".
Mr McGuinness had said unionist parties had allowed "extreme elements" within their community to "set their agenda" during the Haass talks.
He made the comments after the five party leaders met on Tuesday to discuss the failed talks.
The talks, chaired by former US diplomat Richard Haass and Harvard academic Prof Meghan O'Sullivan, ended on New Year's Eve without any agreement on how to deal with contentious parades, flags and the legacy of the Troubles.
On Monday, the assembly rejected a Sinn Fein motion calling for the implementation of the Haass proposals.
Mr Dodds, MP for North Belfast, said Mr McGuinness's comments were "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".
"This is causing enormous damage to community relations," he said.
"Will the secretary of state, urge Sinn Fein to stop wallowing in the filth of murder?"
Mr Dodds's comments were echoed by Ulster Unionist Tom Elliott.
In a statement, the assembly member said Mr McGuinness "could not be more wrong".
"Mr McGuinness's comments smack of petulance and an attempt to deflect from the dysfunctional nature of OFMDFM [Office of the First Minister and deputy First Minister] and the fact that it was he and Peter Robinson who invited Mr Haass and Dr O'Sullivan to Belfast to Chair the talks," he said.
Mr Elliott said the Ulster Unionist Party is keen to see agreement on flags, parades and the past and took part in the talks "in good faith".
"Quite frankly Martin McGuinness is the last person who should be lecturing anyone about extremism, given his role as a leader in a gang of extremists known as the Provisional IRA who tried to bomb this country and its people to bits because they couldn't get what they wanted," Mr Elliott said.
Speaking in the Commons yesterday, Secretary of State Theresa Villiers encouraged all party leaders to continue working on the issues discussed during the Haass talks.
"There is an important opportunity here still to be seized by the political parties to make real progress on these divisive issues by resolving their differences and reaching agreement," she said.
British prime minister David Cameron later told the Commons there was "merit" in the Haass proposals.
Responding to a question from Alliance East Belfast MP Naomi Long, Mr Cameron said: "I noted Peter Robinson described the Haass proposals as providing the architecture for future agreement and discussion.
"I Hope we can take the Haass work, including the very difficult work done on the past, and take that forward with all sides trying to agree."