The protesters forced their way into Dundonald House

A review of security is under way at the headquarters of the Northern Ireland Prison Service after a protest by supporters of republican prisoners.

Up to 30 protesters forced their way past the reception area at Dundonald House in Stormont on Wednesday and made their way to an office on the sixth floor, according to the Prison Service.

Staff called the police but the group were able to get access to Prison Service offices before they arrived.

They were protesting over republican prisoners having to share cells with loyalist inmates.

The Prison Officers' Association said it was worried that sensitive material may have been seen and copied by the protesters.

Association chairman Finlay Spratt said the latest security breach was a disgrace and called for a public inquiry into how it happened.

"Here was an office left vulnerable where all the personal details of prison officers were kept," he said.

"The staff that worked in that office were subjected to brutal harassment and intimidation.

"Therefore the management of the Northern Ireland Prison Service failed to protect them and protect the details of prison officers."

Finlay Spratt has called for a public inquiry

He also said a review of security at the building was not enough but an inquiry should be held into what steps had been taken since a leak of prison officers' details last year.

"The management of the Northern Ireland Prison Service abdicated their responsibility. They haven't a clue what's going on, they don't understand the environment prison officers work under in Northern Ireland.

"They have total disregard and disrespect for prison officers that they allowed this to happen."

The Northern Ireland Prison Service said it was unclear what information the protestors may have seen but it believed no personal details were compromised.

"Thanks to the courage and determination of staff, all confidential filing cabinets were secured," said a spokesman.

Details on hundreds of prison staff were found during police raids in north and west Belfast last October, which were linked to IRA intelligence gathering.

Files found by the police were understood to contain the names and home addresses of almost all 2,000 prison service staff.

The controversy surrounding alleged spying at Stormont led to the suspension of Northern Ireland's political institutions.