Sinn Féin leader Gerry Adams has said he has “grave concerns” following the arrest of his party’s Northern chairman Bobby Storey, who he described as his friend.

Asked if he would describe the arrest as an example of political policing, Mr Adams said the PSNI had to be allowed to conclude their investigation.

“At this stage I don’t want to go any further than to say that I have grave concerns about how all of this has developed, including the arrest of Bobby Storey,” he said.

Mr Storey was one of three men arrested on Wednesday in connection with the murder last month of Belfast republican Kevin McGuigan.

Mr Adams said he would be “shocked” if Mr Storey was not released. He said he valued Mr Storey’s contribution to “our struggle”.

Asked to expand on Mr Storey’s background, Mr Adams said he first met Sinn Féin’s Northern chairman in prison.

“He buried his mother two weeks ago. He’s currently ill and is on leave from the party in terms of his position. He’s a long-standing friend of mine,” Mr Adams said.

“I first met him in the cages of Long Kesh when he was a very young man and the rest of it is a matter of history.”

Asked how Mr Storey had risen to such a prominent position within the party leadership, Mr Adams said he had been elected to his position by the membership of the party.

Mr Storey was a “valued member of our national leadership” and a “person of great integrity” who had worked for both party and for Irish people for a very long time.

“He’s been charged with nothing.”

Meanwhile, Mr Adams insisted an IRA structure did not exist, saying Sinn Féin was the “only one republican organisation involved in the republican struggle and in republican activism”.

Sinn Féin and those who voted for the party were not accountable for “murderers or criminals” who carried out two killings in the North recently.

Mr Adams said he understood the North’s First Minister Peter Robinson had “given an ultimatum” to the Northern Secretary Teresa Villiers to suspend the Northern institutions or the DUP leader would withdraw his Ministers.

“She of course doesn’t have the power to do that,” Mr Adams said.

He said Sinn Féin was opposed to an adjournment of the Assembly. Mr Adams said he was concerned that the institutions “should come down”. He described the institutions as dysfunctional but their absence would be a very serious development because they were now where tensions and arguments were played out.