A Co Donegal politician has denied any involvement in influencing a garda investigation into the disappearance of six-year-old Mary Boyle nearly 40 years ago.

Sean McEniff, who is Ireland's longest-serving politician, issued a statement through his solicitors.

In it, he said that he "emphatically and unconditionally denies that he was the politician who allegedly contacted the gardaí in Ballyshannon at the time of the disappearance of Mary Boyle."

The Fianna Fáil politician has served on local councils for 55 years, including Bundoran Town Council and Donegal County Council.

The statement added: "He has no knowledge of such a call other than what he has heard recently on what was contained in the video 'Mary Boyle, The Untold Story'.

The solicitors said the statement was being issued at Mr McEniff's request, "in relation to the rumour and innuendo surrounding a YouTube video published recently on the internet 'Mary Boyle, The Untold Story'.

Mr McEniff said: "The disappearance of Mary Boyle has been a tragedy for the Boyle family and they are deeply affected by it. The gardaí have conducted detailed and extensive investigations which are continuing and should be co-operated with by all concerned."

The statement said that Mr McEniff supported the call for a Commission of Investigation to be established to investigate all aspects of the disappearance of Mary Boyle.

It added that he had taken legal advice in relation to the defamatory comments made both directly and by innuendo and will take such steps as are necessary to protect his reputation.

"Some of the comments and statements that have been made are false, malicious and damaging to Mr McEniff.

"He will not be making any further public statement and the matter will be dealt with through his solicitors."

Although Mr McEniff was not named on the video, there has been widespread speculation in south Donegal that he was the politician it claimed made a call to a senior garda which resulted in the main suspect not being arrested in the child's disappearance near her grandparents home at Cashelard, Ballyshannon, 39 years ago.

Up to 500 people marched in Ballyshannon on Saturday seeking justice for Mary.

A garda 'cold case' team is due in Ballyshannon soon to investigate the tragedy.