Fianna Fáil leader Micheál Martin has ramped up the pressure on Taoiseach Leo Varadkar by saying he would enter government-formation talks with Fine Gael.
Mr Martin's U-turn on talking to Fine Gael came after he firmly ruled out Fianna Fáil entering government with Sinn Féin.
However, the country is braced for weeks of uncertainty as Mr Varadkar will speak to Mr Martin only as a last resort.
The Fine Gael leader will begin negotiations with Mr Martin only after Sinn Féin and Fianna Fáil fail in their attempts to form a government.
"If Fianna Fáil and Sinn Féin fail in its negotiations then we will consider matters at that point," the Taoiseach's spokesperson said.
With talks set to go on for weeks, the spokesperson also revealed the Government would not be making any "major financial or policy decisions" until a new administration was formed.
Mr Martin yesterday held a four-and a-half hour meeting with his parliamentary party in an attempt to ease tensions after a disastrous General Election campaign.
He sought permission to enter into talks with all political parties - apart from Sinn Féin.
The proposal was supported by the majority of his party but concerns were raised by a group of TDs about doing a deal with Fine Gael.
Asked on RTÉ's 'Six One' whether a grand coalition was now in sight, Mr Martin said it would take a lot of work to create a programme for government.
"Any government that's formed has to be sustainable. I believe a government should be formed,” he said.
“In terms of the future, I can’t be certain how this is going to work. I wouldn’t rule out another election because this is going to be so difficult.”
Mr Martin said each of the main parties would nominate leaders for Taoiseach when the Dáil returned next Thursday but none would succeed.
“We won’t get a resolution next Thursday,” he said. But he added that finding a new government shouldn’t take 70 days like in 2016.
Put to him that he was breaking his pre-election promises on coalition formation, Mr Martin noted Sinn Féin had changed its position from two days ago. “Sinn Féin did say two days ago the last party they want in government is Fianna Fáil and two days later I get a letter,” he said.
Yesterday, Sinn Féin leader Mary Lou McDonald said it would be “quite a challenge” for Fianna Fáil to sign up to the “government of change” she was proposing, but said there was an obligation on the party to consider the matter.
After writing to Mr Martin to seek discussions, Ms McDonald said the position of Fianna Fáil not to speak to Sinn Féin at all was “untenable”.
She also criticised efforts by Fianna Fáil and Fine Gael to form a grand coalition, saying it would be “a slap in the face to the Irish electorate”.
The Taoiseach’s spokesperson said there was a responsibility on Sinn Féin to form a coalition with left-wing parties or with Fianna Fáil and negotiate a “republican socialist programme for government” that “keeps the many promises they have made”.
“In the meantime, the Government will continue with its duties as required by the Constitution and any major financial or policy decisions will be deferred until a new government is formed,” he added.
The Social Democrats last night met Mr Martin after which the party said: “We had a cordial and respectful conversation but our concern is it didn’t sound a lot like change.”
A Green Party source said that while it would hold exploratory talks with all parties, they did not expect substantial developments until next week. “The five main strands for us are how are we going to pay for it all, what are we going do on housing, how are we going to pay for Sláintecare, what are we going to do on climate change and Brexit and the future of Europe.”
Meanwhile, Independent TDs’ attempts to form alliances have seen three distinct groups beginning to emerge with Sligo-Leitrim TD Marian Harkin, a former MEP, seeking an alliance with like-minded independents.
However, this is likely to be separate to the reconstituted Rural Independent Group from the last Dáil, which includes Mattie McGrath, Michael Collins, Carol Nolan, Michael Healy-Rae and Danny Healy-Rae.
However, Tipperary TD Michael Lowry is no longer involved with this group.