A dissident republican prisoner has suffered serious injuries after he was assaulted in Maghaberry jail, Co Antrim by another inmate.
There is no segregation in the prison between republicans, loyalists and non-paramilitary inmates. Tensions in the jail are understood to be high.
A Northern Ireland Office spokesman said the incident was being investigated.
Mr Tommy Crossan (28) from west Belfast says he was making tea on his landing on Tuesday night when he was assaulted. He sustained serious head and body injuries and was treated in the prison hospital.
Mr Crossan is facing charges relating to a gun attack on an RUC station in west Belfast this year. No organisation claimed responsibility but the Continuity IRA is widely believed to have been involved.
Mr Crossan's wife, Ann, claimed the prison authorities had previously guaranteed protection for republican inmates but this promise was now "patently false". She said the prisoners would not be safe until they were segregated.