Kevin McGuigan murder: Police link Provisional IRA to killing in Belfast
Police say they believe Provisional IRA members were involved in the murder of Kevin McGuigan Sr in east Belfast.
Police say the organisation called Action Against Drugs, whose members include members of PIRA, were responsible.
Mr McGuigan Sr, 53, was murdered at his home in east Belfast last week.
Det Supt Kevin Geddes said a major line of inquiry was that members of PIRA were involved.
"Action Against Drugs as you may be aware made a public statement on 6 August that they would execute anybody who had any involvement or they believed had any involvement in the murder of Jock Davison," he added.
"It is my assessment that Action Against Drugs are a group of individuals who are criminals, violent dissident republicans and former members of the Provisional IRA.
"They are dangerous, they are involved in violence and extortion of the nationalist and republican communities and they have a criminal agenda.
"My assessment is that this is a separate group from the Provisional IRA. A major line of inquiry for this investigation is that members of the Provisional IRA were involved in this murder.
"I have no information at this stage to say whether that was sanctioned at a command level or not and I'm not prepared to speculate on that."
Mr McGuigan Sr was murdered at his home at Comber Court in the Short Strand area last week.
Police believe two men shot him several times in the head and chest at point blank range before running off.
Analysis: NI Home Affairs Correspondent Vincent Kearney
The First Minister, Peter Robinson, warned that there would be very serious political repercussions if there was evidence that the Provisional IRA was involved in Kevin McGuigan's murder.
So far, we don't have evidence, we have police saying one definite line of enquiry is that members of the Provisional IRA were involved in this.
Politicians, certainly the DUP, will be very interested in what was said today.
Peter Robinson said last week he intends meeting the Chief Constable George Hamilton to be given an assessment of the likely involvement of the Provisional IRA and I think the first minister will be keen to have that meeting now.
Sinn Féin has previously denied speculation that the Provisional IRA may have been involved in his murder. The DUP said at the time that there would be "repercussions" if that is the case.
At a press conference, Mr Geddes appealed for calm and said it was important that there were no other killings.
"I am very aware of heightened tension and emotions around this investigation and we completely understand that," he added.
"But I would make an appeal for anyone with influence in the community to please accept that influence and let's have some community calm.
"We would appeal for absolutely no retaliation in relation to this murder.
"It is important that there are no other families left feeling the hurt and the pain of the Kevin McGuigan family and the Jock Davison family."
Mr Geddes said several firearms had been recovered in searches and that although the investigation was in its early stages the police were following definite lines of inquiry.
"I would appeal for anybody who may have seen people dressed in dark clothing in the Comber Court, Harper Street or Beechfield Street area around about, just before or just after 20:50 BST on 12 August to please get in touch with us," Mr Geddes added.
He also appealed for anyone with further information that would help with the murder investigation to contact police.