The chairman of the Garda Siochana Ombudsman Commission (GSOC) says he believes the organisation headquarters was under "some form of surveillance".

Simon O'Brien says the Commission investigated possible bugging under a legal clause that allows it to investigate possible offences by members of the gardaí.

But he says he personally decided not to report the suspicions to the Minister for Justice because he did not want to suggest that gardaí had organised the surveillance of the office.

However he is clear that he believes the office was targeted.

GSOC members are before the Oireachtas Public Oversight and Petitions Committee over alleged bugging of their Dublin offices.

Last night one of the Commissioners said the Ombudsman could not definitely rule out the prospect of bugging at its headquarters.

However the government insists there is no proof of any surveillance having been carried out.

The Taoiseach is standing over the government assertion that GSOC was not bugged.

Enda Kenny and the Justice Minister said yesterday that GSOC found no definitive evidence of surveillance at its office in Dublin.

However one of the Commissioners, Kieran Fitzgerald, has said that bugging cannot be definitively ruled out.

The Taoiseach said earlier that while he has not seen the security sweep report, it did not conclude that the garda watchdog was spied on.

Meanwhile the journalist who broke the story is standing by his story. John Mooney of The Sunday Times spoke to Newstalk Breakfast earlier.