Politicians on both sides of the Border have condemned the killing of Paul Quinn.
Two senior Sinn Féin politicians deplored the attack, with the North's Minister for Regional Development Conor Murphy and Cavan-Monaghan TD Caoimhghín Ó Caoláin issuing statements of condemnation.
Mr Murphy said: "There are wild and baseless allegations being made. However, I do not believe that there is any republican involvement in this murder.
"Anyone with information that can assist the family should come forward to the gardaí or PSNI immediately."
Mr Ó Caolain said he was "deeply shocked".
"Whatever circumstances are behind the attack there can be no justification for this type of violence.
"I strongly condemn the attack which took place in my own constituency and urge that anyone with information relating to the murder go to the gardaí immediately.
". . . I also extend my sympathies and support to the people of the area."
SDLP Newry Assembly member Dominic Bradley said the local community in Cullyhanna and Castleblayney felt "utter revulsion" at the killing.
"The community in Monaghan and south Armagh must work with An Garda Síochána and the PSNI by giving them the information they need to bring these people to justice," he said.
He believed that the dead man had been threatened by local Provisionals in south Armagh and that the IRA had also been responsible for severe beatings of at least two other individuals in the area.
Last night the implications of the murder threatened to spill over into the political arena.
Independent unionist MEP Jim Allister, who resigned from the DUP in March over the decision to share power at Stormont with Sinn Féin, said the Quinn family's claims about IRA involvement could not be overlooked.
"The suggestion that the IRA killed Paul Quinn requires absolute clarity from the PSNI and the gardaí, with no phoney distinctions being made between 'organisational acts' and actions by individual IRA members," he said.
A postmortem examination on the body of the 21-year-old murder victim found at a remote Co Monaghan farm is to be carried out this morning.
Members of the Garda Technical Bureau carried out their investigations yesterday at the farm in the townland of Oram about 8km along the road between Castleblayney and Newtownhamilton in Co Armagh.
Officers in white boiler suits examined the scene, while other officers searched nearby fields. The Garda helicopter was also called in.
Deputy State Pathologist Dr Michael Curtis was alerted, gardaí said.
The Quinn family, in a statement issued to BBC Northern Ireland, said their son had been involved in an incident involving a known republican in south Armagh.
A local source also repeated this claim to The Irish Times.
The family statement alleged that the dead man was the victim of an attempted Provisional IRA "exiling" order.
"Our son courageously and correctly refused to leave," they said. "We believe that he was abducted by the Provisional movement and brutally beaten to death."
The killing was also condemned by local Sinn Féin councillor Colman Burns.