The Taoiseach today accused Fine Gael leader Enda Kenny of telling a "barefaced lie" that Mr Ahern is not tax compliant but Mr Kenny repeated his assertion and said it was a "serious" matter that the leader of the country was unable to produce a tax clearance certificate.
Mr Ahern was speaking in South Africa on the first day of a trip to highlight Irish aid projects in the region.
Taoiseach Bertie Ahern
Fine Gael leader Enda Kenny and Labour leader Eamon Gilmore demanded Mr Ahern's resignation at the weekend. Mr Kenny claimed the Taoiseach's accounts of his personal finances had demeaned the profession of politics. Both repeated their attacks on the Taoiseach today.
Although Mr Ahern's staff insisted yesterday he would not take any questions from reporters during the trip about the attack on him yesterday by Fine Gael and Labour, the Taoiseach addressed the issue during a press conference.
Mr Ahern said: "The charges that I haven't paid my tax bill by Enda Kenny is just wrong. He knows he is telling a barefaced lie and he is.
"I have honoured my tax compliance and he's just wrong and he knows he's wrong," he added.
Speaking to the media in Dublin later, Mr Kenny repeated his claims about Mr Ahern's tax affairs and said it was a situation "of his own making".
Mr Kenny reiterated his claim that Mr Ahern was not tax compliant, stating that if in fact the Taoiseach was in compliance, he would have been able to produce a tax clearance certificate.
"I would remind people of what Mr Ahern said about Mr [Charles] Haughey and Ray Burke and Michael Lowry in the Dáil in terms tax matters. It seems to me as if there is one law for Bertie Ahern and another law for the rest of the people."
Mr Kenny also said Mr Ahern had appeared to engage in "censorship of the press" in initally stating he would not answer questions on the matter during his visit to South Africa.
On the accusation from the Taoiseach that Mr Kenny had told a "barefaced lie", Mr Kenny said: "I have no intention of descending to his level of name-calling. This is much too serious a matter that the Taoiseach of our country is unable to produce a tax clearance certificate and be compliant with the Revenue Commissioners."
Mr Kenny was asked whether there might be an innocent explanation for the fact that the Taoiseach had been unable to produce a tax clearance cert.
"He's the person who introduced the law requiring politicians in particular to be able to send out a statement to the Irish people that they are tax compliant. He has not been able to produce a tax clearance certificate and the fact of the matter is that had he paid his taxes when they were due he would not now be in this situation. It is of his own making." he said.
Labour leader Eamon Gilmore today accused the Government of an "unsuccessful attempt to gag the press" during his South Africa visit.
"The whole approach of the Taoiseach and his government colleagues is showing an increasingly strident reaction - bordering on the hysterical - to legitimate questions that have been raised about his financial affairs and his tax issues," Mr Gilmore said.
"I have previously acknowledged the immense contribution of Mr Ahern to Irish public life, not least in his work to secure peace and create new political structures in Northern Ireland. He now risks undermining all this by clinging to office at a time when his credibility has been so undermined and his authority so damaged."
Fine Gael is expected to put down a Dáil motion declaring its full confidence in the tribunal when the Dáil resumes later in January.
Last weekend, Mr Ahern defended his handling of his tax affairs in a statement and criticised the leaking of his tax affairs to the media. He said it would be inappropriate for him to discuss the details "with anybody other than the Revenue Commissioners".
He claimed he did not get the "same confidentiality, the same fair hearing, and the same circumstances in a tribunal as anyone else".
Mr Ahern told RTÉ last week he had paid a sum on account to the Revenue Commissioners pending the outcome of discussions on his tax affairs.
The sum is believed to be of the order of €70,000.
As an elected public representative, he must declare that he is tax compliant to the Standards in Public Office Commission (Sipo) by the end of February. Oireachtas members are required within nine months of election to furnish a tax-clearance certificate, or a statement that issues remain to be resolved.
Last week, Mr Ahern said he had made a statutory declaration to Sipo to the effect that he was, and is, "to the best of my knowledge and belief in compliance with my tax obligations".
"That is my position. That will, I am confident be evidenced in due course by the issue of a tax clearance certificate," The Taoiseach added.