Former taoiseach Bertie Ahern has resigned from his political party in the wake of a corruption inquiry, but insisted the findings of the probe had dealt him a grave injustice.

The Mahon Tribunal into the Republic of Ireland's planning process accused Mr Ahern, one of the architects of the Northern Ireland peace process, of not telling the truth in regard to a number of financial transactions in the 1990s.

His Fianna Fail party had been due to vote on a motion to expel him and other colleagues named in the report next week - but his announcement has pre-empted that move.

"The last thing I want to do, given that I have now retired as a public representative, is to be a source of political division in the party I care so deeply about," he said.

"I appreciate the support that party members have pledged to me unprompted in the past week.

"I have decided the best way that I can now serve Fianna Fail is to tender my resignation as a member of the party."

Mr Ahern, who revealed his decision in an article for Ireland's Sunday Independent, said leaving Fianna Fail was a "political decision" and insisted it should not be interpreted as an admission of wrongdoing.

He said he left with "immense sadness and genuine regret" but also with a deep affection for the grassroots members of the party.

The inquiry shamed a series of senior figures in Fianna Fail, once considered the dominant, establishment party in Irish politics.

It did not brand Mr Ahern, the leader of three coalition governments, as corrupt but refused to accept any explanations he offered for a quarter of a million of bank lodgements he made in the early 1990s.

The tribunal panel sat for over 15 years, heard 900-plus days of public sittings and conducted extensive forensic financial trawls.

It left Mr Ahern's political legacy shattered - none of his evidence for lodgements of more than IR£250,000 between 1993 and 1995 were accepted.

The inquiry also warned it could not find where some money came from.

Current Fianna Fail leader Micheal Martin said achievements by Mr Ahern, like the Good Friday Agreement of 1998, were real and enduring but could not absolve him from facing the implications of the report.

He had called for him to be expelled from the party ranks.

But Mr Ahern has signalled an intent to challenge the findings of the tribunal, claiming they were not infallible.

"This week has been an extremely difficult and emotional one for me," he said.

"I am hurt and disappointed by the findings of the Mahon Tribunal.

"At the outset, I want to make it clear I have done nothing wrong or dishonest.

"I never took a corrupt payment from anyone and I told the truth to the Mahon Tribunal about my finances and the difficult personal circumstances I found myself in.

"I believe a grave injustice has been done to me.

"I bear the members of the Tribunal no ill-will. They faced a daunting task. But their findings in relation to me are not correct. They are plain and simply wrong.

"I have to be true to myself. It would be far easier for me to say nothing and try to forget about this nightmare.

"But I can't allow this blemish on my character to go unanswered. What has been said about me is erroneous, unwarranted and unjust.

"And I am under no doubt these findings have damaged my reputation.

"I am now actively considering my options as to how I can and I will vindicate my good name."