The two leaders focused on the draft Withdrawal Agreement
The Taoiseach Leo Varadkar has told British Prime Minister Theresa May that the European Union must have the detail of a 'backstop option', in case a full Brexit deal is not reached.
Mr Varadkar and Mrs May have spoken about the latest developments in the Brexit process.
The two leaders spoke by phone on Monday evening.
They discussed Brexit and, in particular, the draft Withdrawal Agreement.
Both Mr Varadkar and Mrs May said they want the options, as set out in the December Joint Report, to be examined in detail.
This would include the preferred option of a satisfactory solution to the border problem being found within the overall future relationship between the EU and the UK.
Mr Varadkar also repeated the necessity, from the EU side, to have the detail of the backstop option of full regulatory alignment spelled out in the draft legal text of the Withdrawal Agreement.
The Office of the Taoiseach has said this option would only come into effect if agreement on one of the other options is not reached.
The pair also "took stock" of the latest situation in Northern Ireland and their recent contacts with the parties, the Taoiseach's office added.
The call came after British Labour Party leader Jeremy Corbyn said his party would support a new customs union with the EU after Brexit.
His comments mark the party's most concrete support for a 'soft Brexit' to date.
Mr Corbyn said earlier: "Labour would seek a final deal that gives full access to European markets and maintains the benefits of the single market and the customs union as the Brexit Secretary, David Davis promised in the House of Commons, with no new impediments to trade and no reduction in rights, standards and protections."