A major IRA intelligence gathering operation in Belfast has been broken up by police, according to the acting deputy chief constable Alan McQuillan.

Speaking at a news conference on Monday, Mr McQuillan, who is to act as deputy chief constable of the PSNI until the Policing Board formally appoints someone in the new year, said he had nothing to suggest the IRA had any intention to use the information in any offensive way.

Mr McQuillan said the breakthrough followed the investigation into the break-in at Belfast's police headquarters in Castlereagh in March.

He said the investigation had taken the police "into the very heart of the Provisional IRA".

Alan McQuillan: Said the operation brought police to the heart of the IRA

Thousands of documents and hundreds of computer disks are being examined by 40 detectives who are working on the Castlereagh case and the alleged IRA intelligence gathering operation at Stormont.

"There are a large quantity of documents apparently copied or stolen from government offices," he said.

"We also have recovered with the documents a significant number of documents that have originated within the Provisional IRA itself.

"A small number of those appear to relate to matters concerning agents working for the provisional IRA within government."

IRA approaches

Northern Ireland's power-sharing executive was suspended on 14 October following a row over allegations of IRA spying within the Northern Ireland Office.

Mr McQuillan added that he wanted to address the concerns of Catholic civil servants.

"We are very conscious that some people working within government who are decent, honest people may well have been approached and may well have had pressure put on them to provide information," he said.

Lives have undoubtedly been saved by police actions

Ian Paisley Jnr DUP assembly member

He said evidence available to the police suggested that IRA approaches may have been made to a very small number of people only.

Sinn Fein's Gerry Kelly said the statement by Mr McQuillan was an exercise in "damage limitation" and showed the police were on the defensive in relation to the Stormont investigation.

However, DUP assembly member Ian Paisley Junior congratulated the police on the operation.

"The revelations by ACC McQuillan that the police have now uncovered active IRA spying activity is another signal that their political counterpart in Sinn Fein is not fit for government.

"Lives have undoubtedly been saved by police actions," he said.

Meanwhile, a civil servant questioned last week by police investigating IRA intelligence gathering at Stormont has been suspended on full pay.

The man was released on Friday without charge.

A spokesman for the Office of the First and Deputy First Minister at Stormont confirmed that a member of staff had been suspended while the police inquiry continued.

The arrested man had access to the Stormont offices of former first minister David Trimble, the Ulster Unionist Party leader, and SDLP leader Mark Durkan, the former deputy first minister.

Four people, including Denis Donaldson, head of Sinn Fein's administration at the Northern Ireland Assembly, were charged last month after police seized documents in raids on republican homes.