Mr David Trimble has urged the Taoiseach to confirm publicly there has been no cover-up of an alleged IRA spy operation on his Government.
The UUP leader has demanded Mr Ahern make a public statement on reports that Republicans have targeted senior members of Fianna Fáil.
He said: "We are calling at this stage for the Irish government to officially state its position. We must make sure there's no cover-up going on at the moment.
"If they find that a senior minister and other Fianna Fáil backbenchers are being targeted by Republicans they need to look into this".
With British Prime Minister Mr Tony Blair and Mr Ahern putting pressure all the parties in Belfast to break the deadlock in the Northern Ireland peace process, Mr Trimble was expected to boycott talks later this week.
The UUP leader insists that the main business involves Downing Street securing a major move on weapons from the IRA that will end the stalemate and help restore the suspended power-sharing administration at Stormont.
But he added that he would hold off making a final decision about attending the talks until he had heard from the Dublin government on the report in yesterday's Sunday Independentnewspaper.
SDLP leader Mr Mark Durkan urged Mr Trimble to attend the talks rather than boycotting them over one issue of concern to his Ulster Unionists.
PA