The Fianna Fáil leader Micheál Martin has criticised Sinn Féin, claiming it is "unacceptable" as a government party.
He was speaking after Sinn Féin President Gerry Adams announced he will step down as leader next year.
Speaking at his party's Ard Fheis, he said: "We will grow even stronger in the future. But leadership means knowing when it is time for change.
"That time is now. I will not be standing for the Dáil in the next election."
In response, at the Fianna Fáil President's Dinner in Dublin on Saturday night, Mr Martin said: "Today's Sinn Fein has always been about putting the Provisional movement first.
"The party is much more than the person and the party remains as unreformed and as unsuitable for government as ever.
"I take no satisfaction in saying that, 20 years after the ceasefire, Sinn Féin is unacceptable for us as a government party.
Gerry Adams after speaking during his presidential address at the Sinn Fein Ard Fheis in the RDS Dublin | Image: RollingNews.ie
"As our members reaffirmed at the Ard Fheis, for Fianna Fáil they are not and will not be a possible partner.
"And just in case people want to waste their time speculating on this not really being the position, please go back to 2015 and 2016 and look at the acres of newsprint devoted to the claim, often anonymously sourced, that we would run into government with Fine Gael.
"We are the only party in Dáil Éireann which after the election did exactly what it promised it would do. We kept our word then and we will keep it again.
"So please, let’s have an end to talk about them being a partner and instead let’s talk about the substance of why they are unsuitable as partners.
"They will change their leader, but the core of the Provisional movement’s approach to politics remains and has been constantly reaffirmed by all of their prospective leaders.
"They might be new leaders but they are not new faces."
"Spare us the idea that we are getting a new departure or a new generation from Sinn Féin. Instead of wasting time about their future political strategies, they need to be held to account for their actions today", Mr Martin added.