The Taoiseach has said a 'backstop' agreement to avoid a hard border in Ireland has to be part of the withdrawal agreement between the EU and UK.
Leo Varadkar has arrived in Brussels for a two-day summit with other EU leaders, with Brexit negotiations a major part of the agenda.
EU leaders have reached a deal with British officials on a transition period after the UK's exit from the bloc, but differences are said to remain over Ireland.
The 'backstop' refers to an earlier deal reached between the UK and EU in December, saying a “common regulatory area” will be established in Northern Ireland following Brexit if no other solutions to the border issue can be found.
A draft version of the agreement was rejected by Theresa May in February as unacceptable, but the British Prime Minister has since told EU leaders that she remains committed to the December deal.
Arriving in Brussels, Leo Varadkar welcomed that renewed commitment.
He observed: "I very much welcome the fact that a protocol that had been ruled out a few weeks... that the British government now accepts that there has to be a 'backstop' in the withdrawal agreement.
"Everyone does share the objective - Ireland, the EU and the United Kingdom - to avoid a hard border. It's now accepted that a backstop has to be in the withdrawal agreement... but we've always said that we're willing to examine alternative solutions, particularly solutions that would bring the UK closer to the EU."
'The right deal'
Mr Varadkar pointed out that October is the deadline for a withdrawal deal to be agreed between the EU and UK, in order for it to become law before the UK's planned withdrawal in March 2019.
He explained: "Everyone takes the view that we'll have to have the withdrawal treaty agreed by October, because it will have to be ratified by the British parliament and the European parliament, and potentially by some national parliaments.
"Would I like to have it done by June? Absolutely. But I would rather have the right deal in October, rather than any deal in June."
He also reaffirmed 'absolute, unconditional' Europe-wide support for the Irish position in Brexit negotiations.
He added: "There is a real understanding, I think, across the European Union that it's important that the EU demonstrates that it supports a small member state that is staying - even if that means not being able to support a large member state that is leaving."
As well as Brexit, issues such as strained relations with Turkey and the Salisbury attack are on the agenda for EU leaders today and tomorrow.