The EU has reiterated the Brexit withdrawal deal is not up for renegotiation but, in its text at the conclusion of Thursday's summit, underlined the Irish backstop would only be temporary should it come into force and pledged to work "expeditiously" to get in place a replacement should it come into force.
European Council president Donald Tusk and European Commission President Jean-Claude Juncker gave a joint press conference in Brussels late on Thursday night.
A text was published on the conclusions of the summit. It said preparations would intensify on all possible outcomes.
It stated the European Council was committed to the agreement reached in November - which has seen the Conservative party tear itself apart and Theresa May face a leadership challenge and the Commons unite against the deal.
Earlier this week Theresa May pulled her meaningful vote on the deal as there was not enough support to see it through. After seeing off a Tory rebellion on Wednesday Theresa May travelled to Brussels to seek assurances on the deal.
Mr Tusk said: "Today Prime Minister May informed the leaders about the difficulties with ratifying the deal in London and asked for further assurances that would at least in her view unlock the ratification process in the House of Commons.
"After discussing the Prime Minister's intervention among the 27 leaders, and bearing in mind our full respect of the parliamentary process in the United Kingdom, we have agreed the following: first, the European Council reconfirmed its conclusions of the 25th November 2018 in which it endorsed the Withdrawal Agreement and approved the Political Declaration.
"The Union stands by this agreement and intends to proceed with its ratification. It is not open for renegotiation."
The text stated it wanted to "establish as close as possible a partnership with the United Kingdom in the future," and was ready to begin work on a trade deal once the document was signed off. Jean-Claude Juncker also said the UK
It said the backstop was needed to prevent a hard border on the island of Ireland and to ensure the integrity of the single market.
"It is the Union’s firm determination to work speedily on a subsequent agreement that establishes by 31 December 2020 alternative arrangements, so that the backstop will not need to be triggered," the text stated.
"The European Council also underlines that, if the backstop were nevertheless to be triggered, it would apply temporarily, unless and until it is superseded by a subsequent agreement that ensures that a hard border is avoided.
"In such a case, the Union would use its best endeavours to negotiate and conclude expeditiously a subsequent agreement that would replace the backstop, and would expect the same of the United Kingdom, so that the backstop would only be in place for as long as strictly necessary."
The text continued: "The European Council calls for work on preparedness at all levels for the consequences of the United Kingdom’s withdrawal to be intensified, taking into account all possible outcomes."
European Commission president Jean-Claude Juncker urged the UK to tell the EU what it wants in the future relationship.
He said: "We also think that in terms of the future relationship our UK friends need to say what they want, instead of asking us to say what we want and so we would like within a few weeks our UK friends to set out their expectations for us because this debate is sometimes nebulous and imprecise and I would like clarifications.
"As we don't know what the collective reactions will be from the Europe 27 and the UK, the Commission on the 19th December will publish all the information that is generally useful for the preparation of no deal, this is preparedness."
Mr Juncker added that he was "still of the opinion that Mrs May is fighting hard and bravely but we have not seen results".
"We would like a peaceful relationship with the UK for the years (to come) but in particular we don't want the UK to think there can be any form of renegotiation whatsoever.
"We can add some clarifications... but there will be no renegotiations."