The RUC Chief Constable, Sir Ronnie Flanagan, has said he believes republican paramilitaries were responsible for the murder in north Belfast of a Protestant taxi-driver, Mr Trevor Kell.
The killing on Tuesday night was followed the next day by separate gun attacks on two Catholics in which a workman, Mr Gary Moore, was killed and a taxi-driver was critically injured. The UDA has been blamed for both shootings.
Sir Ronnie said he had no doubt loyalists were responsible for the gun attacks on the two Catholics, but it was too soon to specify which group.
RUC and British army sources had previously blamed loyalists for killing Mr Kell. The UDA and the UVF were on the brink of formally ending the loyalist feud, and one theory was that the killing was carried out by dissident UDA elements in order to stop an official truce.
Other security sources blamed the attack on the UVF and said Mr Kell had been mistaken for a UDA man. However, speaking on the BBC Hearts And Minds programme last night, Sir Ronnie effectively ruled out loyalist involvement, saying: "In relation to the murder of Mr Kell, while we believe that to have been carried out by republicans, it is too soon to say whether any of the formalised republican terrorist groups were involved."
Sir Ronnie said it was possible the killing was carried out by "renegade' or "freelance" republicans.
Sinn Fein last night insisted loyalists were responsible. Mr Gerry Adams said there was no evidence of republican involvement and called on the RUC to release the forensics of the murder weapon.
In a statement to Ulster Television yesterday, the "Real IRA" Belfast Brigade was quoted as denying involvement in the Kell killing and urging nationalists to remain vigilant. However, sources along the Border close to the "Real IRA" leadership denied all knowledge of the statement, which they said had not been authorised by the leadership.
The North's First Minister, Mr David Trimble, said the recent violence was "a painful reminder that we have some way to go before we finally achieve lasting peace and stability".
Two church leaders yesterday called for the violence to end. The Church of Ireland Primate, Archbishop Robin Eames, warned that recent shootings "could drag us back so easily through a spiral into the darkness". The Catholic Bishop of Down and Connor, Dr Patrick Walsh, said: "It is appalling. People are shocked by what has happened."
The Alliance deputy leader, Mr Seamus Close, urged the Northern Secretary, Mr Peter Mandelson, to make a clear statement on the status of the loyalist ceasefires following the shootings.
He said the authorities appeared to accept that attacks by the paramilitaries against members of their own community were not treated as breaches of their ceasefires.