The top civil servant at the Department of Justice has refused repeated requests to discuss the resignation of Martin Callinan as Garda Commissinoner.

Brian Purcell has told the Oireachtas justice committee that he could prejudice the Fennelly Inquiry if he discusses the matter.

Mr Purcell was the civil servant sent to Martin Callinan's home on the night before he resigned.

Mr Purcell issued an apology to the Garda whistleblowers for how their complaints were treated, but refused to discuss his meeting with Mr Callinan which led to his resignation.