UK PM Theresa May is to deliver a keynote speech next week
Taoiseach Leo Varadkar has said the British government needs to clearly layout its Brexit plans, and that "real detail" is needed - not just aspirations.
He was speaking ahead of a European Union summit in Brussels.
EU leaders are informally meeting to discuss issues including the European Parliament's composition after the 2019 elections, and how the EU appoints top positions.
British Prime Minister Theresa May is to deliver a keynote speech setting out her vision for Britain's future relationship with the EU on Friday, March 2nd.
Mr Varadkar said this needs to give clarity on the issue.
"I'm looking forward to hearing the Prime Minister's speech next week and I really hope that we're going to hear something new and a lot more detail.
"I really think we need - at this stage - real detail as to what the United Kingdom's position is, what new relationship they want the United Kingdom to have with the European Union and have that spelt out in detail, not in aspiration".
Mr Varadkar said he and Mrs May have spoken on the phone and met in person over the last 10 days.
"But based on previous speeches that she's made, if she's going to say something significant about Ireland she would usually let me know in advance.
"If not, then we may speak afterwards - but there's an open line of communication there".
Mr Varadkar added: "The United Kingdom can have as close a relationship with the European Union as it wants - but it's not an 'a la carte'.
"It's not possible to be aligned with the European Union when it suits and not when it doesn't - that's not possible.
"So I think the United Kingdom really needs to square that circle, and it doesn't appear to me that that circle has yet been squared.
"But hopefully when the Prime Minister speaks next week the United Kingdom will be more clear about what it wants in terms of the new relationship and will back that up with real detail - detail that can be written into a legal treaty with the European Union.
"I think we're well beyond the point of aspirations and principles - we need details now".