Allegations of IRA activity leaked against Gerry Adams and Martin McGuinness has already been played out in public, Sinn Fein has said.
But according to the latest US diplomatic cables released by WikiLeaks, the Irish government had "rock solid evidence" the top republicans had advance knowledge of the infamous Northern Bank raid.
Mr Adams and Mr McGuinness said the claims were not new, and they released a party letter which denied the allegations in 2005, while they also sought to blame political rivalries for the episode.
Officials in Dublin told the US ambassador James Kenny that Mr Adams and Mr 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.
The leak attributed the claims to the then Irish prime minister and Fianna Fail leader, Taoiseach Bertie Ahern.
But in a joint statement, released in the aftermath of the WikiLeaks documents, the Sinn Fein leaders said: "We both absolutely rejected these unfounded allegations at the time and do so again today.
"We publicly and privately challenged the Taoiseach to produce evidence to support his allegations. He didn't. We told him they were groundless and untrue. It was and is our view that this had more to do with the electoral rivalries between Sinn Fein and Fianna Fail.
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."
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.