Theresa May is to hold talks with the Northern Ireland political parties amid warnings an expected deal with the Democratic Unionists (DUP) to prop up her minority government will undermine the peace process.
The Prime Minister will meet separately with representatives of Sinn Fein, the Ulster Unionists, the SDLP and the Alliance Party - as well as the DUP - in Downing Street in an attempt to allay growing concerns.
It follows warnings - including from former prime minister Sir John Major - that the Government will compromise its stated impartiality in the province if it enters a confidence and supply deal with the DUP at Westminster.
The nationalist Sinn Fein and SDLP and the cross-community Alliance have all made clear Northern Ireland Secretary James Brokenshire cannot chair the ongoing process to restore power-sharing at Stormont due to the perceived conflict of interest.
The 1998 Good Friday Agreement - also referred to as the Belfast Agreement - commits the UK and Irish Governments to demonstrate "rigorous impartiality" in their dealings with the different political traditions in Northern Ireland.
Sinn Fein's Stormont leader Michelle O'Neill said: "I will be making it very clear that any deal between the Tories and the DUP cannot be allowed to undermine the Good Friday and subsequent agreements."
Mr Brokenshire insisted the Government would honour its commitments in the Good Friday Agreement and warned that time was running out if power-sharing was to be restored and a return to direct rule from Westminster avoided.
"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.
"There is very little time left. An agreement to restore devolved power-sharing government in Stormont must be reached by the 29 June deadline.
"Ultimately, I think the parties understand people voted in the March Assembly elections for a strong voice at Stormont.
"Northern Ireland's political leaders now have it in their hands to take control and shape a brighter future for everyone in Northern Ireland."
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.
It is thought that an announcement on an agreement will be delayed as a result of the Grenfell Tower tragedy - and may not come until next week.
Ministers have already said that the Queen's Speech may have to be set back from its scheduled date of next Monday June 19, because of the ongoing negotiations.
DUP leader Arlene Foster, who met Mrs May in No 10 on Tuesday, is understood to have returned to Northern Ireland leaving her deputy Nigel Dodds to represent the party at Thursday's meeting.
The proposed deal would see the DUP back the Conservatives in votes on the Budget and on any confidence motion while other matters would be negotiated on an issue-by-issue basis.