Fine Gael Leo Varadkar has acknowledged his party is lagging behind in the polls but said the General Election is "all to play for".
Speaking on the BBC's Andrew Marr show, he said: "It's looking like a very tight election."
He added: "We're a bit behind, but everything is within the margin of error of 3%, so this election is all to play for.
The latest Business Post/Red C poll suggests that Sinn Féin has increased its support and is now tied in first place with Fianna Fáil.
Mr Varadkar said: "One thing that won't happen, you won't see a coalition involving my party and Sinn Féin. That's just not going to happen.
"Sinn Féin, in our view, is soft on crime and also high on tax - proposals to tax business, pensions, incomes, wealth, property, you name it, to the tune of four billion euro and that would be enormously damaging for the Irish economy, for people's jobs and incomes and livelihoods and businesses.
"That's definitely not going to happen. So, the likelihood is actually going to be quite difficult to form a government over the next couple of months."
Meanwhile, Mr Varadkar has suggested that Sinn Féin leader Mary Lou McDonald should be included in the RTÉ Prime Time Leaders' Debate on Tuesday night.
Canvassing in Athlone in Co Westmeath, he was asked if he believed that in light if the most opinion poll the electorate would be best served by her inclusion, he said: "I've never had any objection to including Mary Lou McDonald in the debate and I've made that clear from the very start. It is a matter for the broadcasters so it is their decision to make."
He added: "As I've said before, and I'll say again, I have no objection to Mary Lou McDonald taking part in the debate and that's a matter for the broadcasters. And, I think it would be useful to take such an opportunity to scrutinise Sinn Féin policies a bit more."
Describing the roll-out of high-speed broadband across Ireland as "21st century decentralisation", Mr Varadkar said opponents in the Department of Finance "wouldn't bat an eye" at spending the money needed on transport in Dublin "which only benefits half as many people".