Micheál Martin has denied he only remains Fianna Fáil leader by "default" because there is nobody else ready to take over.
Despite losing six straight Dáil by-elections, he insisted he was still best placed to lead run the party.
Positioning the party at the centre-left, Mr Martin branded Fine Gael a right- wing party as he attacked Taoiseach Enda Kenny over his stance on the North.
Mr Martin told a party gathering that it would be “a disgrace” if Mr Kenny had told UUP leader Mike Nesbitt that Stormont was “not our business”.
The intervention followed claims by Mr Nesbit that the Taoiseach told him: “The Irish Government’s role would not touch on internal Stormont issues.”
Mr Martin said: “Neither Albert Reynolds or any Fianna Fáil Taoiseach or minister who followed him would ever have agreed that the affairs of Northern Ireland are not our business.
“According to the Ulster Unionist Party leader, this is the very assurance he was given by Enda Kenny last week.
“If it is true it is a disgrace and a direct abandonment of the dynamic central to every major achievement of the peace process.”
Mr Martin also used the party’s annual Wolfe Tone memorial to attack the provisional IRA, saying: “In 30 years of their illegitimate campaign, they never won more than a fraction of the Irish public to their side.
“They have caused incredible damage to republicanism by their illegitimate campaigns of violence, waged in the face of the opposition of the over-whelming majority of Irish citizens and where the interests of their organisations have been put ahead of the interests of the Irish people.”
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