"There is a unity of objective among people in the United Kingdom", May said following a meeting with French President Emmanuel Macron in Paris.
May is holding talks Thursday with other Northern Ireland political parties amid warnings the expected DUP deal will undermine the peace process.
Local TD Gerry Adams visited 10 Downing Street yesterday where he told British Prime Minister Theresa May that she is in breach of the Good Friday Agreement.
"The UK Government is offering whatever support we can, working alongside the Irish government, as appropriate, honouring our respective commitments in the Belfast Agreement to serve the interests of the whole community in Northern Ireland", he said.
Former prime minister David Cameron said May needed to listen to opposition parties, and that there would be pressure for a softer Brexit that would give greater priority to a close trading deal with the EU.More news: Qatar opens new shipping routes via Oman amidst Gulf ban
More news: Brooks Koepka wins US Open with 67 in final round
More news: No change on 'Dreamers' program
The EU's chief Brexit negotiator Michel Barnier also warned Tuesday that time was passing. That's why we're ready to start very quickly.
Seven MPs were elected in Sinn Féin colours last week, although the party has always refused to take up seats in Westminster.
Guy Verhofstadt, the European Parliament's chief Brexit negotiator, warned Tuesday that "the current uncertainty can not continue" and on Wednesday issued five "pressing questions" on Twitter. "There's a lot of anxiety", Sinn Fein MP Michelle Glidernew told.
With the two-year clock on Brexit ticking since March, when a letter from May formally started proceedings, Barnier dismissed the suggestion of postponing the negotiations and said such a delay would only prompt further instability.
France's Macron said the EU's door was still open for Britain as long as the negotiations were not finished, but that it would be hard to reverse course.
Resolutely anti-Brexit, The Liberal Democrats campaigned for a second referendum on the terms of Britain's withdrawal from the EU.