The Taoiseach has accused Fianna Fáil of not always being whole-hearted in its support for the Government's approach to Brexit.
Leo Varadkar said the party was wrong when it accused the Government of overselling the political agreement on Brexit it secured in December 2017.
"Now their new narrative is that we are inadequately prepared for no deal. The truth is no country can be fully prepared for no deal," he said.
Mr Varadkar was speaking at a Fine Gael meeting to select Frances Fitzgerald and Mark Durkan as the party's candidates for the European Parliament Elections in the Dublin constituency.
He was again strongly critical of Fianna Fáil and Sinn Féin over the events leading up to Ms Fitzgerald's resignation as tánaiste and justice minister in late 2017.
He said the parties often make happy bedfellows.
The Taoiseach claimed they "shamefully" joined forces to try to hound Ms Fitzgerald out of public life.
He said they threw out wild accusations that were later shown to be false and which they knew at the time were false.
"Sinn Féin and Fianna Fáil should hang their heads in shame. And even at this late stage, they should apologise and take back what was said," Mr Varadkar said.
However, the Taoiseach said he did recognise the role Fianna Fáil has played in providing political stability given the uncertainty of Brexit.
"It stands in stark contrast to the division and chaos at Westminster," he said.
The Taoiseach also pledged that nobody would see a dramatic increase in their property tax next year.
He said the vast majority of homeowners will not see any increase at all and added it was simply a case of adjusting the tax bands upwards to reflect the upward increase in property prices.
At a meeting of the Fine Gael Parliamentary party, which was also held tonight, the Taoiseach told members that the party has established a Northern Ireland engagement group.
The group is to be chaired by the Louth TD Fergus O'Dowd and will develop links with parties and groups in Northern Ireland, attend party conferences as well as cultural, economic and academic events.
The group will also organise meetings on issues relating to Northern Ireland and will look at ways to raise Fine Gael's profile there.