Gardaí have admitted that the Commissioner, Noirin O'Sullivan, used a Gmail account for work business.

But in a statement this evening they have insisted that the Commissioner's systems are secure and there is no evidence that they have ever been compromised.

The force has claimed that the account was used "due to restrictions with the Garda email system such as e-mail size and storage".

"The Commissioner occasionally used a Gmail address to ensure that Garda business has been discharged effectively," it said.

The statement added that Noirin O'Sullivan is aware of her obligations protect national security and policing operations, and would under no circumstances allow them to be compromised.

"At all times, there has been due regard to the sensitivity of the information being transmitted" using the Gmail account, it said.

The statement also appeared to confirm that Gmail accounts are set up for senior Gardaí, to use on work mobile devices, as a matter of routine.

It said the current Garda policy on email use dated from 2012, and did not take into account the fact that most modern smartphones now require a commercial email address in order to access full functionality.

The Commissioner is to compile a report on the issue and submit it to both the Policing Authority and the Department of Justice.

The Authority today confirmed it would be investigating the matter. O'Sullivan was due to attend a public hearing with the Authority on Thursday to discuss other matters, including the O'Higgins Report.

Details of the email usage first emerged in yesterday's Sunday Times, which reported that O'Sullivan's Gmail account was linked to a Dropbox account which was compromised in a cyber attack in 2012.

That was denied by Gardaí earlier today, when the force said there was no evidence of any of O'Sullivan's accounts or files being compromised.