The protesters forced their way into Dundonald House

The material was on a desk when the protesters entered the sixth floor offices at Dundonald House in Stormont on Wednesday.

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

A prison service spokesman said up to 30 protesters forced their way past the reception area and made their way to the sixth floor.

Staff called the police but the protesters were able to get access to the offices before they arrived.

The spokesman said: "It is unclear, at this stage, what information they might have seen, but to the best of our knowledge no personal details were compromised.

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

An urgent review of security at the prison service has been launched.