Image copyright PA Image caption Bobby Storey is the northern chairman of Sinn Féin and a "valued member" of the party's leadership

Well-known republican Bobby Storey has been arrested over the murder of former IRA man Kevin McGuigan Sr.

Mr McGuigan Sr was shot dead at his home in east Belfast last month, and police said members of the Provisional IRA were involved in the killing.

Mr Storey was one of three men, aged 59, 45 and 58, arrested by police in north and west Belfast on Wednesday.

The other two arrested, Eddie Copeland and Brian Gillen, are also well-known republicans.

Mr Storey, a former IRA prisoner, is the northern chairman of Sinn Féin.

In 2005, Ulster Unionist Party (UUP) MP David Burnside told the House of Commons under parliamentary privilege that Mr Storey was the head of intelligence for the IRA.

Image copyright Pacemaker/BBC Image caption Bobby Storey (left), Eddie Copeland (centre) and Brian Gillen (right) are leading republicans

Mr Storey is a close ally of Sinn Féin president Gerry Adams and has an office at Stormont.

Defender

Sinn Féin's Martin McGuinness said he was "surprised" to learn about Mr Storey's arrest.

"Bobby Storey is a valued member of Sinn Féin's core leadership," the deputy first minister said.

"He has played a leading role in the development of Sinn Féin's peace strategy and is a long-standing and loyal supporter, defender and advocate of the peace and political processes.

"We look forward with confidence to his early release."

The Police Service of Northern Ireland's Chief Constable George Hamilton said last month that Provisional IRA members had a role in Mr McGuigan Sr's murder.

Image caption Members of the Provisional IRA were involved in the murder of Kevin McGuigan Sr, police said

But he added there was no evidence at that stage that the killing had been sanctioned at a senior level of the organisation.

Sinn Féin said the IRA no longer exists after it ordered an end to its armed campaign in 2005.

Adjournment

A total of 16 people have been arrested in connection with Mr McGuigan Sr's murder.

One person has been charged, while the others were released unconditionally.

After Wednesday's arrests, First Minister Peter Robinson tweeted: "These events were predicted in my statement on Monday.

"No-one can be above the law. That is why we sought adjournment of the assembly.

Image copyright Pacemaker Image caption Police officers carried out a search of a house in west Belfast after the arrests

"We will do so again. Hopefully the UUP will support us this time, rather than voting with Sinn Féin for business as usual," he added.

UUP leader Mike Nesbitt said the "political implications could not be more serious and profound".

He said his MPs would meet Prime Minister David Cameron on Wednesday to discuss the arrests.

Sparked

"That is how serious it is being treated in Downing Street," he added.

The UUP leader said he had no prior knowledge that the arrests were going to be made, but said he had been "given to believe that the situation could become blacker".

In 2001, Mr Robinson told the House of Commons that Mr Gillen was a member of the IRA's ruling army council.

Image copyright Pacemaker Image caption Martin McGuinness (right) said Sinn Féin was confident of an "early release" for Bobby Storey

Mr Copeland is a leading republican from north Belfast.

In 1994, former UUP leader David Trimble used parliamentary privilege in the House of Commons to describe him as an IRA godfather.

A year earlier, he was seriously injured when he was shot by a soldier, and has survived a number of attempts on his life by loyalist paramilitaries.

The three men are being questioned at Antrim police station.

Exceptional

The murder of Mr McGuigan Sr sparked a crisis in Northern Ireland's power-sharing government after the police assessment of IRA involvement.

The UUP said Sinn Féin's denial that the IRA existed made it "impossible to do business with them" and subsequently left the Northern Ireland Executive.

The Democratic Unionist Party said there would be no more meetings of the executive unless in "exceptional circumstances".

A fresh round of talks between the main political parties got under way on Tuesday.