SDLP leader Mr Mark Durkan is to brief US special envoy Mitchell Reiss on the killing of a man in a Belfast bar that has been blamed on members of the IRA.
Robert McCartney (33), a bouncer and father of two, was stabbed to death during a fight at Magennis's Bar on January 30th. Even though detectives have questioned several men, including a top republican, no one has been charged with the killing.
SDLP leader Mr Mark Durkan
Mr Durkan met Mr McCartney's family last night after they publicly blamed members of the Provisional IRA for the killing.
Mr Durkan said today: "His vicious murder was at the hands of IRA people, including a very senior IRA person who was centrally involved in the attack.
"Many of those IRA people have been prominent Sinn Féin election workers and minders for their politicians.
"The family are not claiming that this was a planned IRA operation. They are very clear that the full force of the IRA has been used to intimidate witnesses and prevent the killers from being brought to justice."
It has been alleged that the IRA is shielding the gang involved in the attack.
Police have refused to comment on claims that Magennis's Bar was forensically cleaned by republicans who warned witnesses against saying anything.
"The family are equally clear as to why Robert was killed. Simply because he refused to bend the knee to a Provo boss," Mr Durkan added.
"This is the worst kind of oppression by the IRA of their own community. It is a frightening example of the Mafia culture that is tearing away at our communities and threatening decent people. The family have asked me to take this case up and I gave them my word that I will do so," he said.
"I will be meeting US special envoy Mitchell Reiss on my US visit this week and I will be briefing him on this appalling murder and the organised cover-up and intimidation that is occurring."