The Taoiseach has said he would not rule out working with any party after the next election but accused Sinn Féin of being in “destructive opposition mode”.
Fianna Fáil leader Micheál Martin also said he found it extraordinary that Sinn Féin had been “absolutely silent” on the Russian build-up of troops on the Ukrainian border, accusing it of being “anti-European Union”.
A number of opinion polls have seen Sinn Féin open up a clear lead as the most popular party in Ireland under leader Mary Lou McDonald.
Asked about whether he would be open to working with Sinn Féin after the next election, Mr Martin said: “We will contest the election in our own right as a political party with our own policies and ideas and after that general election, we will consider, first of all, where we are in terms of our own seats and numbers of seats, and where others are.
“My sense of Sinn Féin at the moment is that it’s in a very destructive, resolute opposition mode, opposing everything that moves literally, politically.
“The level and range of what they’re promising is in the billions at this stage, and doesn’t, frankly, add up.
“A lot of their policies don’t add up, their housing policies don’t add up.”
The Taoiseach continued: “The other aspect of it that worries me a bit is their international, European policy.
“I think at heart, they’re still an anti-European Union party.
"I was struck in the Dáil in the debate leading into the European Council, for example, they were absolutely silent on the massive Russian military build-up on the Ukraine (border).
“I found that extraordinary.
"I've noticed this for the last number of years, Sinn Féin will never criticise Russia, always remain silent."
Mr Martin predicted that the next Government in Ireland would not be easy to form.
He said: “There needs to be far greater focus on the actual substance of policy.
"Now, we managed to get agreement with the Greens and Fine Gael around fairly weighty topics, one being the climate change one, which has been a significant feature of government.
“All I’m simply putting to you is that the next government won’t be that easy to form, because it will have to be formed around policies and substance and issues and ideas.
“I’ll rule nobody out.
“I was simply pointing out that there are very substantive policy issues that go to the heart of what this country is about, and has been about for 50 years, and when I listen to Mary Lou (McDonald) she damns the last 50 years.
“So I believe that they would fatally undermine, with their current policies, the enterprise base of this in this country.” – PA
