Image caption DUP leader Peter Robinson said he had engaged in an initial discussion with the PSNI chief constable

The Democratic Unionist Party has raised the prospect of Sinn Féin being excluded from the Stormont executive following an ex-IRA man's murder.

It comes after police said they believe Provisional IRA members were involved in Kevin McGuigan's murder last week.

That was rejected by Sinn Féin who said the IRA "had left the stage".

On Friday, the police said a 60-year-old man had been arrested in east Belfast in connection with the murder.

DUP leader Peter Robinson said he would have discussions with other Northern Ireland parties "about tabling the necessary exclusion motion in the assembly and asking the secretary of state to intervene in circumstances where the evidence points to the IRA being involved".

He said he had had an initial discussion with the Police Service of Northern Ireland (PSNI) Chief Constable George Hamilton.

Mr Robinson said that before the return of the assembly from recess, his party would seek a further update from Mr Hamilton "to establish his conclusion regarding those responsible and the role of those in the republican movement who are associated with Sinn Féin".

Analysis: Political Editor Mark Devenport

The power of exclusion that First Minister Peter Robinson wants to talk to other parties about is contained in the 1998 law that put the Good Friday Agreement into effect.

The power is designed to be used if the assembly or the Northern Ireland Secretary thinks a Stormont party or one of its ministers is in breach of their commitments to non-violence, peace and democracy.

Politicians found to be in breach can be excluded from office for periods between three and 12 months. Read more.

"As I indicated in my press briefing last week there can be no place for terror and murderous activity on our streets and republicans cannot be in the executive in circumstances where this murder was the work of the Provisional IRA," he added.

DUP MP Gregory Campbell said that independent assessment was needed on the IRA's status and that the party would also be seeking a meeting with the Northern Ireland Secretary Theresa Villiers.

'Reality and fact'

DUP Finance Minister Arlene Foster said it was a "very serious time for power-sharing in Northern Ireland".

She said what was needed was to establish "reality and fact" to determine if the Provisional IRA was still operating behind the scenes.

"It is very concerning to think that so-called units may still be in existence or may be stood up at a time when they're needed to deal with so-called internal matters," she said.

"Murder is murder and it cannot be in any way at the heart of what we do in Northern Ireland."

Police said on Thursday that an organisation called Action Against Drugs, whose members include members of the Provisional IRA, were responsible for Mr McGuigan's killing.

Image copyright Pacemaker Image caption Kevin McGuigan Sr was shot dead at his home at Comber Court in east Belfast last week

Sinn Féin North Belfast MLA Gerry Kelly said the IRA no longer existed and asked for a meeting with Mr Hamilton.

He described the PSNI's statement as "contradictory".

"The IRA has gone, it has left the stage, it made a statement in July 2005, saying it was gone," Mr Kelly added.

He said the police assessment that members of the Provisional IRA were involved in Mr McGuigan's murder was wrong.

"In that same statement the chief inspector said that the AAD, the Action Against Drugs was the organisation he believed was involved," he said.

"I am a republican. I am saying this is a criminal gang. I think I may have the credibility to be able to know the difference."

'Stark statement'

Sinn Féin's Martin McGuinness, who is Northern Ireland's Deputy First Minister, said those who killed Mr McGuigan and Gerard 'Jock' Davison were criminals and "must be brought to justice".

UUP leader Mike Nesbitt said he thought it was a "stark statement" from the PSNI that could not be "allowed to linger in the public domain without further investigation and further explanation".

SDLP leader Dr Alasdair McDonnell said he welcomed the assessment by the PSNI and would be seeking an urgent meeting with the chief constable.

Image caption North Belfast MLA Gerry Kelly said he believed the PSNI statement was contradictory

Alliance leader and Justice Minister David Ford said police comments that members of the Provisional IRA were involved in the murder had the "potential to be extremely serious", but urged caution before people started "jumping to conclusions".

"This is at the very early stage of an inquiry into an absolutely appalling murder with a family still grieving just a day or two after they buried their loved one," he said.

"What we need is information, proper intelligence, so the facts can be established by the police and then the political implications will need to be considered if there are links to the IRA."

'Exit door'

Traditional Unionist Voice leader Jim Allister said it was "time for unionists who work the Belfast Agreement to face up to reality".

He said it was time to show Sinn Féin the "exit door from government".

"I accept the reality that a senior police officer has said that it is his belief that current IRA members were involved in this heinous murder," he said.

"Now if there are current IRA members, then there's a current IRA.

"If the IRA exists then Sinn Féin has a paramilitary wing, and what place in government is there for a party with a paramilitary wing, that's how elementary this is."

UKIP leader in Northern Ireland, David McNarry, said the PSNI's assessment left "no room for Sinn Féin to manoeuvre politically".

'Great concern'

The Northern Ireland Office said as the murder was currently under investigation by the PSNI "it would be inappropriate to comment further at this stage".

The Police Federation for Northern Ireland (PFNI) said the PSNI assessment over who was responsible for murdering Mr McGuigan was a cause of "great concern" to officers.

In a statement, PFNI chairman, Mark Lindsay, said: "This was a deliberate and measured assessment by the PSNI, conscious that every syllable would be placed under the microscope and weighed and analysed.

"It is a very worrying development if a command structure can be activated at will. Our members view developments with great and justifiable concern."

In a statement, the Irish government said: "What is important now is that the PSNI be allowed to complete their investigation and obtain evidence that would enable the persons involved be brought to justice. (It is not helpful to speculate on any other potential issues until that process is complete)."