Peter Robinson has fiercely rejected an allegation from Martin McGuinness that he was guilty of cowardice of the worst kind in not condemning the crimes of loyalist paramilitaries.
During Assembly question time, Stormont's first minister delivered a stinging response to his partner in government's claim - in another clear indication of the increasingly fraught relationship at the heart of the power-sharing institutions.
Earlier this month, the Sinn Fein deputy first minister alleged that DUP leader Mr Robinson and other unionist politicians had been reluctant to link the UVF to attacks against both foreign nationals and the offices of the Alliance party in his east Belfast constituency.
Mr McGuinness claimed Mr Robinson was motivated by fear of losing votes in working class loyalist areas in this week's European and local government elections.
Answering an Assembly question from party colleague Jonathan Craig, Mr Robinson insisted he condemned the actions of anyone involved in criminal acts.
He then launched a strident attack on Sinn Fein, claiming he would not take lectures on cowardice from a party linked to the IRA.
"I will tell him (Mr Craig) what I do believe to be cowardice of the worst kind - that's those who shoot people in the back and have done so in the past," he said.
Tensions between the DUP and Sinn Fein over a range of disputes on big ticket issues facing the Executive have, perhaps expectedly, appeared to intensify in the lead up to the elections.
Mr Robinson branded Mr McGuinness's comment as "synthetic" and claimed it was designed to deflect the attention that had been shone on his party's past in the wake of the arrest of Gerry Adams in connection with the 1972 murder of Belfast mother-of-ten Jean McConville.
Sinn Fein president Mr Adams, who vehemently denies any involvement in the killing, was released earlier this month after four days of questioning pending a police report being sent to prosecutors for assessment.
During the episode, Mr McGuinness had indicated Sinn Fein would review its support for the Police Service of Northern Ireland if Mr Adams had been charged.
However Sinn Fein did make clear statements of support for the PSNI after Mr Adams was released.
Mr Robinson claimed Mr McGuinness was trying to shift focus from his comments on the PSNI.
He then referenced Mrs McConville's murder as he attempted to turn Mr McGuinness's rebuke back on republicans.
"It's the cowardice of those who take out a young woman, in the midst of her family, a widow with ten children, take her away and torture her, tie her hands behind her back and then shoot her in the back of the head - that's cowardice of the worst kind," he said.
The DUP leader then challenged the Sinn Fein Assembly members sitting on the opposite benches to raise their hands if they believed the IRA had exhibited cowardice.
None of them obliged.
"Not one, Mr Speaker," Mr Robinson continued, as he listed a number of other notorious IRA attacks.
"Not one would say that those who tied a bomb to the window of the La Mon hotel and then had a napalm-style effect on those who had gone to enjoy a dinner for the Collie Club - that is cowardice of the worst kind. Those who planted a bomb at a Remembrance Service in Enniskillen - that's cowardice of the worst kind.
"Those who would stop a vehicle with workmen returning home at Kingsmill (shooting ten dead) - that's cowardice of the worst kind. So I will not take lectures from anybody on the issue of cowardice."
Mr McGuinness later issued a statement responding to Mr Robinson's remarks in the chamber.
"During my time as Deputy First Minister, I have tried to avoid recriminating about the past," he said.
"In response to Peter Robinson's comments today I could raise many issues around unionist politicians involvement in the Ulster Workers strike, collusion with loyalist paramilitaries and the setting up and import of arms by Ulster Resistance.
"But in retreating into the past, Peter Robinson misses entirely the point.
"When I talk about a failure of leadership and political cowardice, I am talking about the here and now. I am talking about the failure of unionist leaders to stand shoulder to shoulder with the rest of us in denouncing the squalid sectarian and racist violence of the UVF. The failure to name and condemn the UVF. The attempts to divert attention and implicitly excuse the UVF in a quest for extreme loyalist votes.
"I have stood shoulder to shoulder with unionist leaders in condemning the activities of so called dissident republicans. We have not seen the same united approach in response to UVF-orchestrated violence against isolated members of our ethnic minority communities, against the small nationalist community of the Short Strand, against the PSNI during the flag protests or against Alliance party offices."