Theresa May will meet European leaders and EU officials later today (Tuesday) for talks aimed at rescuing her Brexit deal.
She will hold talks with Dutch PM Mark Rutte and Germany's Angela Merkel after postponing MPs' final vote on the deal.
The UK PM has said she needs "further assurances" about the Northern Ireland border plan to get Commons backing.
European Council President Donald Tusk insisted the EU would "not renegotiate" but said leaders would discuss how to help "facilitate UK ratification".
Work and Pensions Secretary Amber Rudd said further talks with Brussels would focus on the Brexit "backstop" on the Irish border, which Mrs May earlier admitted had caused MPs "widespread and deep concern".
The PM's abrupt U-turn - after days of repeated insistence that the vote would go ahead - prompted Labour leader Jeremy Corbyn to secure a three-hour emergency debate on Tuesday.
"It cannot be right that the government can unilaterally alter the arrangements," said Mr Corbyn, who earlier accused Mrs May of "losing control of events".
No date has been set for the Brexit deal to again be put before MPs, although Mrs May indicated the final deadline for the vote was 21 January.
Leading Conservative Brexiteer Jacob Rees-Mogg said Mrs May lacked the "gumption" to put her "undeliverable" deal before MPs.
He is trying to get enough Tory MPs to submit letters of no confidence in the PM to trigger a leadership contest.
The Times reported that Crispin Blunt became the 26th MP to do so on Monday.
"I want to encourage those who are thinking about it; get it done," Mr Blunt told the paper.
Forty eight Conservative lawmakers must submit letters for any challenge to be initiated.
In other Brexit developments:
- A Labour backbencher was expelled from the Commons after grabbing the ceremonial mace in protest
- Former prime minister David Cameron insisted he had no regrets about calling the referendum, saying he had "made a promise" to do so
- The Brexit secretary said policy "had not changed" despite a European court ruling the UK could cancel Brexit without permission from the other 27 EU members
What next for Mrs May?
The prime minister told MPs on Monday that a number of European leaders had "indicated that they are open to discussions to find a way to provide reassurance" over the backstop.
However, Irish Prime Minister Leo Varadkar said it was not possible to renegotiate the Irish border backstop proposal without "opening up all aspects" of the Brexit withdrawal agreement.
And Mr Tusk pointed out in a tweet that time for discussion was running out.
European leaders were already due in Brussels at a summit on Thursday but Mr Tusk's spokesman said they would now meet specifically to discuss how to prepare for a no-deal scenario.
Mrs May will set off on another intense round of diplomacy before then, travelling to The Hague and Berlin to meet her Dutch and German counterparts on Tuesday.
She will then meet Mr Tusk and European Commission president Jean-Claude Juncker in Brussels.
The BBC's Brussels reporter Adam Fleming said Mrs May was "trying get more legal oomph behind the language" in the withdrawal agreement about the EU using "best endeavours" to get a trade deal which would remove the need for the backstop to be used.
