Mrs May will meet with Sinn Fein, the Ulster Unionists, the SDLP and Alliance Party in separate engagements at Downing Street on Thursday afternoon.
"There was an update on the on-going talks with the DUP", the Prime Minister's official spokesman said.
Parliament now "deserves a say", he said, adding that there was "perhaps an opportunity to consult more widely with the other parties on how best we can achieve it".
Soon after the meeting, May set off to the House of Commons where MPs were reconvening for the first time after the June 8 general election and overwhelmingly re-elected John Bercow as the Speaker of the House.
Labour Leader Jeremy Corbyn has close ties to Sinn Fein and the Sinn Fein MPs are understood to be hoping that in return for their support, Mr. Corbyn would back a call for a referendum on Northern Ireland leaving the United Kingdom and joining Ireland.
The negotiations with the DUP revolve around support from the party on a vote-by-vote basis in parliament, rather than a formal coalition government.
"There is wide spread concern that Theresa May in seeking a deal with the DUP to remain in office will make the job of re-establishing the Executive more hard".
The EU negotiator said the special nature of the Republic of Ireland and Northern Ireland would be a key element of the talks.
Former British Prime Minister John Major said he was concerned May's plan to govern with the support of the DUP could pitch the province back into turmoil by persuading "hard men" on both sides of the divide to return to violence.
Seven MPs were elected in Sinn Féin colours last week, although the party has always refused to take up seats in Westminster.
"This new arrangement is very unsettling and people are concerned and anxious about what it may mean, or what promises may be given. There's a lot of anxiety", Sinn Fein MP Michelle Glidernew told AFP. "I am dubious about it", Major, who served as prime minister from 1990 to 1997, told BBC radio.
Any hard border, he said, would be catastrophic.
"It's passing quicker than anyone believes".
The UK's Brexit minister, David Davis, will open divorce talks in Brussels next week with an offer to allow the three million European Union citizens living in Britain the same rights that they have now, the Financial Times reported on Wednesday.
Ms May made clear the Brexit negotiations would begin on schedule despite the political uncertainty at home.
The Europeans have also insisted that no talks can start on a trade deal until the issue of payments to the EU by Britain are resolved, another position previously rejected by Theresa May.
"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.
"We've had some very good discussions today and those discussions are continuing this afternoon", she said.
As talks go on, the European Union unveiled plans to give itself new powers over London's banking business after Brexit, in what could be a blow to the city's supremacy as a global financial hub.