Mary Lou McDonald has warned the Green Party that facilitating a Fianna Fail/Fine Gael government would create considerable public anger in Ireland.
The Sinn Fein president cautioned Greens leader Eamon Ryan that doing business with those parties would be a “mistake”.
Ms McDonald’s comments come amid ongoing efforts to form a government three weeks after the inconclusive general election result.
She also declined to be drawn on whether a coalition deal between Sinn Fein and Fianna Fail would be more likely if Micheal Martin was not leader – insisting questions about her rival party’s leadership were “entirely a matter for themselves”.
Sinn Fein is still trying to form a left-leaning government with like-minded parties and independent TDs in the Dail, but will struggle to reach the 80 seats required for a majority.
Fianna Fail, which like Sinn Fein currently has 37 parliamentary seats, is also trying to form an administration, and has held tentative discussions with Fine Gael, which has 35 seats.
Fianna Fail and Fine Gael have repeatedly ruled out going into government with Sinn Fein.
The Green Party, which has 12 seats, has held talks with both Sinn Fein and Fianna Fail over the potential of entering government as a junior coalition partner.
Ahead of a meeting of her party’s ruling council in Dublin on Saturday, Ms McDonald said: “One thing is very clear – people did vote for change and whatever way you might interpret that it certainly was not a vote to return a Fianna Fail/Fine Gael government.”
The republican leader said her party had “constructive” talks with the Green Party during the week.
Asked about the Greens’ discussions with Fianna Fail, she added: “I have said publicly and privately to the Greens I think that any move to put Fianna Fail and Fine Gael back together in government is a mistake.
“I think it would cause considerable disappointment and indeed considerable anger amongst the public, certainly for that more than 50% of people who voted for Sinn Fein, and others, with an eye to a new government and to what we would describe as a government of change.”
Ms McDonald was asked about a comment made from the floor at one of her party’s post-election rallies during the week when someone described the Greens as “Fine Gael on bikes”.
The party president acknowledged that the comment might not have gone down well with Green Party members, but she insisted it was meant as a joke.
“I think for those who were at the meeting it was said in a way that certainly I took as light-hearted,” she said.
“It was certainly not meant to be an insult to them.”
Ms McDonald added: “I think the person who made that comment was making it in mirth. Much as Fine Gaelers take offence at being described as ‘blue shirts’ but nine times out of 10 that is said as a light-hearted almost throwaway remark. But I accept that also might cause offence to some of them.
“We are called lots of things too and we have to take that on the chin equally.”