The Taoiseach Enda Kenny says Micheál Martin and Fianna Fáil cannot be trusted in government.
His comments come after a new poll shows Mr Kenny and Micheál Martin are neck-and-neck when it comes to approval ratings.
24% of those surveyed say they would be happy with either man as Taoiseach.
The latest IPSOS/MRBI poll for the Irish Times was carried out last Friday and Saturday, among 1,200 adults at 100 sampling points in all constituencies.
When asked 'Which of the four main party leaders they would prefer to see as Taoiseach?', 24% of those surveyed opted for both Enda Kenny and Micheal Martin.
Gerry Adams received 12% support, followed by Joan Burton on 4%. The margin of error is 2.8%.
But Enda Kenny says Fianna Fáil cannot be trusted.
The Taoiseach also says the convention he is proposing to look at the issue of abortion should be chaired by "an appropriate woman".
Mr Kenny says the issue is one "he struggles with" himself.
He says the citizens convention needs to deal with whether the 8th amendment is removed from the constitution in a way that takes politics out of it.
Meanwhile, campaigning continues as we enter the final days of the election campaign before voters go the polls on Friday.
The government parties have been saying all along that this is the time when people will make up their minds - and tonight's final TV debate on RTÉ has the potential to swing voters.
The leaders of the four main political parties will take part, amid complaints from the smaller parties about their exclusion from the debate.
Party policies
Today on the campaign trail, Fine Gael and Labour are both talking jobs.
Labour will also launch their sports policy. Sinn Féin will detail their plan for public service spending.
Meanwhile, Fianna Fáil are discussing how to improve pension provision.
The Anti Austerity Alliance-People Before Profit group will set out their plans to repeal the 8th amendment.
The Social Democrats will launch their youth manifesto. Renua will look at homelessness and mortgage arrears, as part of their build a better society document.
And the Green Party will list their climate change proposals.
