Democratic Unionist leader Arlene Foster has warned the Taoiseach that it is not appropriate for him to chart the future of negotiations to restore Stormont powersharing.
Mrs Foster insisted that role lay firmly with the UK government.
She was reacting to a suggestion from Leo Varadkar that the UK and Irish governments might table their own joint proposals as a way to break the political deadlock in Belfast.
While she chided Mr Varadkar for his comments in relation to Stormont, Mrs Foster welcomed other remarks made by the Taoiseach in which he acknowledged his government's stance on Brexit may have angered unionists.
Mr Varadkar, who in a speech in Washington DC yesterday called for redoubling of efforts to restore devolution after Easter, suggested such an intervention could be a means to forge a deal between the DUP and Sinn Fein.
Fourteen months after powersharing collapsed, the two parties remain at loggerheads on a range of cultural, social and legacy disputes.
Mrs Foster said it was not for the leader of the Irish Republic to suggest the next steps in efforts to restore powersharing.
"In keeping with the principle of consent and the three-stranded approach (framework of the Good Friday Agreement) it is not appropriate for the Irish Prime Minister to outline future political steps relating to Northern Ireland and a resumption of talks," she said.
Mr Varadkar elaborated on his suggestion as he continued his St Patrick's Day tour of the US on Wednesday.
"What I intend to do after Easter once this intense phase of Brexit passes with the EU summit at the end of the month, is to propose a new engagement with the British government for us to try once again after Easter to secure an agreement between the major parties and also all the parties in Northern Ireland," he said after an event at the US Chamber of Commerce in Washington.
In a wide-ranging speech at an event on Capitol Hill on Tuesday to mark the 20th anniversary of the Good Friday Agreement, the Taoiseach moved to reassure unionists who have been angered by his government's approach to Brexit.
He acknowledged some comments might have been viewed as unwelcome or intrusive.
"If that is the case, I want to make it clear that it certainly was not our intention," he said.
"I want to repeat that we have no hidden agenda."
The Irish government's efforts to maintain a soft border, in particular, its demand that Northern Ireland continues to align with many EU regulations, has angered unionists who fear it is veiled attempt to push a united Ireland agenda.
Mrs Foster welcomed Mr Varadkar's remarks.
"I recognise and welcome the acknowledgement that many unionists have felt some actions and statements from the Irish government have not been helpful," said Mrs Foster.
"In the past I and other DUP ministers did build up good and productive relationships with our counterparts in the Republic which was to the benefit of both countries. I hope the Taoiseach's comments can represent a return to that more positive working relationship."