Garda Commissioner Nóirín O'Sullivan has said that she was "not aware" of any private meeting between former garda commissioner Martin Callinan and former Public Accounts Committee chairman John McGuinness.

Deputy McGuinness told the Dáil last week that the former commissioner had requested the meeting in a hotel car park and that, during it, he attempted to undermine the credibility of garda whistleblower Sergeant Maurice McCabe.

Earlier, Sinn Féin deputy leader Mary Lou McDonald called on Commissioner O'Sullivan to outline if she had any knowledge of the meeting.  

Ms Lou McDonald said that she believes that Deputy McGuinness should have brought to the O'Higgins Commission of Investigation details of the meeting he had with Mr Callinan two years ago.

Today, Deputy McGuinness said he accepted that his information may have helped the commission's investigation into whistleblower allegations.

Speaking on RTÉ's News at One, Ms McDonald called for an immediate response from Mr Callinan on the issue.

She also called on Mr McGuinness to outline what the former commissioner said to him about Sgt McCabe.

She said as a member of the PAC at the time, she was not aware of this meeting or the content of what was said to Mr McGuinness.

She added there was "merit in the concern" expressed by Mr McGuinness that to reveal details of the meeting before Sgt McCabe gave his evidence to the PAC may have derailed the process as there was "no appetite within the system to have Sgt McCabe appear before the committee".

Earlier, Mr McGuinness said he is "vindicated" in his decision to speak out now about the meeting with Mr Callinan two years ago.

Speaking on RTÉ’s Today with Sean O'Rourke, he said he wanted to ensure Sgt McCabe gave his evidence before the PAC when efforts were being made to stop him from coming before it.

Mr McGuinness said he allowed the report by the O'Higgins Commission to proceed because he believed Sgt McCabe would be exonerated.

He said he "accepts that it may be the case" that this information about this meeting could have helped Judge O'Higgins in his deliberations.

However, he said if he brought forward the information about this meeting at the time, it "may very well have scuppered the whole Public Accounts Committee inquiry".

Mr McGuinness said: "What has transpired after that in leaked documents and so on, is the fact that the garda commissioner, it is reported, set out to destroy the credibility of Maurice McCabe and his integrity.

"And because that happened, I felt that it had to be put on record that this meeting happened and during all of this time, there was an effort made at senior level within the force to undermine not only Maurice McCabe, but many others who have brought forward vital information into how their work is being done."

The Fianna Fáil TD said that "serious questions remain unanswered including is there a continued culture to cover up within the gardaí force, the whistleblowers that are under siege in that force".

However, he said he had "made the call having heard the O'Higgins report, and having listened to the debate that it was time to put on record a piece of proof that the culture within the force continued in the vein that militated against Sergeant Maurice McCabe".

Minister for Jobs, Enterprise and Innovation Mary Mitchell O'Connor, meanwhile, has said Mr McGuinness probably should have revealed earlier that he had had the meeting.

Asked if he should have revealed the meeting at the time, she said: "Should he have? I probably would have thought he would have."

She said she was a "little surprised" to hear about the meeting but said it was up to Mr McGuinness to explain.