The killing of a man in Co Monaghan could jeopardise the North's powersharing arrangements if it is linked to the IRA, the DUP has warned.
Paul Quinn (21)
The family of Paul Quinn (21) has blamed the Provisional IRA after the victim was fatally attacked in a rural Border area. Mr Quinn, from Cullyhanna, Co Armagh, died shortly afterwards in hospital.
His family claimed he had previously been involved in an altercation with the IRA and was ordered to leave the country - but refused.
Further claims today have suggested that Mr Quinn met his death as a result of "two petty incidents" involving members of a prominent republican family.
"Clearly if the IRA has been involved in some way in the murder of Mr Quinn then that will have very serious consequences in terms of the political process," DUP MP Jeffrey Donaldson said.
Northern Ireland's First Minister, the Rev Paisley Snr, added this evening: "If this murder was the work of the Provisional IRA then very serious consequences will flow from that. As a Party we have made it clear that there will be no place in government for those associated with murder.
"I encourage everyone to wait for the findings of the police, both in Northern Ireland and the Irish Republic.
"There will be no fudging of this issue and everyone must work to ensure that those responsible for such a callous murder are exposed and brought to justice."
DUP MP Jeffrey Donaldson
Sinn Féin president Gerry Adams earlier denied republican involvement and called on anyone with information about the murder to make it available to police on both sides of the Border.
He said he was deeply shocked and claimed the death was linked to fuel smuggling involving criminals.
Mr Adams added: "The criminals responsible for this dreadful killing must be brought to justice. I do not believe that there was any republican involvement in this murder."
Taoiseach Bertie Ahern urged full public co-operation in the hunt for the murderers and agreed with Mr Adams that the attack looked to be linked to criminal activity.
"Whatever about the past of some of these individuals, I think this appears to be associated with local criminal activity and the important thing is that everybody condemned it, the important thing is that that everybody urges everybody to communicate and to help the Garda investigation and that's now underway," he said.
PSNI security sources said they could not be sure who was to blame at this stage. "Nobody could go into a witness box and state definitively one way or another," a police source said.
However, former senior Sinn Féin member Jim McAllister claims the attack followed rows with republicans in the south Armagh area.
"It happened from two petty incidents is the general belief in this area, two very minor incidents," Mr McAllister said. "He [Paul] got involved in an altercation with another young lad who'd be of a prominent republican family a couple of months back. And more recently he got involved with another republican in this area also.
"None of them [the incidents] warranted anything remotely resembling this kind of an attack."
Mr McAllister dismissed the suggestion the attack could have been sparked by a dispute over diesel laundering. "Total nonsense. Diesel launderers are wealthy men. Diesel launderers have plenty of money and the lifestyle to go with it," he said.
Former Labour leader Pat Rabbitte also warned of a major political fallout if there was any involvement by the Provisionals.
The gardaí and PSNI are investigating the death. A Garda spokeswoman said the postmortem would be carried out at Our Lady of Lourdes Hospital in Drogheda, Co Louth.