Taoiseach Leo Varadkar said comments made by new British Prime Minister Boris Johnson about the Irish backstop are “not in the real world” saying the two administrations are “at odds”.
On taking office Mr Johnson at Downing Street declared: “Never mind the backstop, the buck stops here.”
He talked of setting about negotiating a new deal but that was immediately rejected by Mr Varadkar.
Mr Johnson said Brexit would happen in October "no ifs, no buts", adding "the buck stops here".
"The doubters, the doomsters, the gloomsters" who said it could not be done were "wrong", the new PM added.
However, his comments drew stinging criticism from Mr Varadkar who said Mr Johnson's comments were “clear cut but certainly not detailed.”
“Confidence and enthusiasm is not a substitute for a European policy or a foreign policy. So we will need to hear in detail what he has in mind. I think what I would like to do is hear from him, to put some flesh on the bones of what he said today,” Mr Varadkar said.
The Taoiseach said any suggestion of Mr Johnson being able to deliver a new deal before the Halloween deadline was simply out of the question.
I got the impression that he wasn't just talking about the backstop but rather a whole new deal. That is not going to happen.
"The EU council doesn't meet until October 12, we have no plans to meet any earlier. Any suggestion that there could be a whole new deal negotiated within weeks is totally not in the real world,” the Taoiseach added.
In his first address as Prime Minister, Mr Johnson said that he will succeed in delivering Brexit by the Halloween deadline “no ifs or buts”.