Meanwhile, talks are continuing between the DUP and Conservatives, to secure the support of the DUP's 10 MPs in steering government business, including crucial measures on Brexit, through the Commons.
After more than an hour of talks between Mrs May and DUP leader Arlene Foster on Tuesday, Mrs May said the discussion had been productive.
A Downing Street source told the Press Association that the talks had been "constructive" but refused to put a timescale on when they would conclude.
Before travelling to the French capital, Mrs May had been leading the talks with the DUP.
Before her departure for France, Mrs May had addressed MPs in the Commons, calling on Parliament to "come together in a spirit of national unity". The Prime Minister will also meet the other Northern Ireland parties, the SDLP, the Ulster Unionists and the Alliance.
Sinn Fein's Michelle Gildernew (Fermanagh and South Tyrone) raised concern about an alliance, saying: "This new arrangement is very unsettling and people are concerned and wary of what it may mean, and what promises will be given or promises extracted from Theresa May".
Northern Ireland's main parties are expected to hold talks with the prime minister in Downing Street later.
According to BBC, a deal between both parties was supposed to be announced on Wednesday thereby helping May form government in the United Kingdom after her party emerged as the largest party in the recently concluded elections but failed to win a majority.
The EU's chief Brexit negotiator Michel Barnier also warned Tuesday that time was passing.
"My preoccupation is that time is passing, it is passing quicker than anyone believes because the subjects we have to deal with are extraordinarily complex", he added.
"But, let us be clear and organized and once the negotiations have started we should be well aware that it'll be more hard to move backwards", he noted.
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.
He said: "I'm sure we all look forward to welcoming the Queen's Speech just as soon as the coalition of chaos has been negotiated".
Liberal Democrat MP Alistair Carmichael said: The Conservatives can not go from weak and wobbly to business as usual in three days.
"The Tory civil war on the European Union which has ripped it apart since the Maastricht rebellions of the early 1990s, and which the referendum was supposed to solve, is now raging again", said Chris Grey, an academic who specialises in Brexit at Royal Holloway college in London.
With formal European Union divorce talks due next week, May heads to France on Tuesday to meet Emmanuel Macron, who last month swept to victory in the presidential election.
The SDLP MLA Claire Hanna said: "It is a calm and rational comment from somebody who played a generally honourable role here".
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