Gerry Adams has denied claims on WikiLeaks that he was an IRA leader and had advance knowledge of the infamous Northern Bank raid.
According to the latest US diplomatic cable leaks, the Irish government had "rock solid evidence" on the allegations.
But Mr Adams said the claims were not new, that he had denied them at the time, and blamed Irish political rivalries with his Sinn Fein party for the allegations.
Mr Adams and Martin McGuinness were aware that the £26.5 million robbery at the Northern Bank in Belfast in 2004, which was blamed on the IRA, was going to be carried out, officials in Dublin told the US ambassador James Kenny.
But Mr Adams said the claims were made publicly by the then Irish Premier and Fianna Fail party leader, Taoiseach Bertie Ahern, and were denied by republicans at the time.
"I repudiated it then, as did Martin. It isn't true," said Mr Adams.
"I then spoke to the Taoiseach privately about this matter.
"It was my conviction at the time, because there was very intense, as there is now, electoral rivalry between Sinn Fein and Fianna Fail.
"I saw this and still see this as part of Fianna Fail's attack on or fight back against Sinn Fein at that time."
He said that despite WikiLeaks attributing the information to US diplomatic cables, the issue was never raised in Sinn Fein contacts with the White House.
"I worked very closely with, and indeed still work very closely with, American ambassadors and the US president at the time, vice president and other members of the administration going back 15 years or so," said Mr Adams.
"They never raised this with me."
Mr Kenny's cable referred to a meeting with a senior Irish government official which focused on Mr Ahern's concerns about the peace process.
The ambassador recorded: "He said that the GOI (government of Ireland) does have 'rock solid evidence' that Gerry Adams and Martin McGuinness are members of the IRA military command and for that reason, the Taoiseach is certain they would have known in advance of the robbery."
While Mr McGuinness, Stormont's Deputy First Minister, has admitted being an IRA commander, Mr Adams has long denied he was even a member of the organisation.
The WikiLeaks claim, reported in the Guardian newspaper, comes as the Sinn Fein president prepares to take a political gamble by resigning his Westminster seat in west Belfast to stand in Co Louth in the Republic of Ireland's forthcoming election.
The move is part of Sinn Fein's strategy to build its electoral support south of the border.
A party spokesman dismissed the claims last night as "utter nonsense".
"There is not a shred of evidence linking republicans to the Northern Bank robbery and Martin McGuinness and Gerry Adams have both made their positions crystal clear in relation to these matters in the past," he said.
Mr Adams later told the BBC he rejected the claims.
Meanwhile he said documents, also from WikiLeaks, which suggested that MI5 had files on the murder of solicitor Pat Finucane, were an important disclosure.
Mr Adams said if files exist, they should be released.