(CNN) - German Chancellor Angela Merkel had a stark message for Theresa May on Tuesday: The Brexit deal cannot be renegotiated.
The embattled British Prime Minister met the German leader in Berlin as she embarked on a desperate mission to win concessions from European leaders in an effort to sell the deal to the UK Parliament.
German lawmakers briefed by Merkel after the meeting said that while there may be room for maneuver on the nonbinding political declaration that accompanies the Brexit deal, there was no question of reopening the legal text itself.
"There is absolutely no room for renegotiation of the withdrawal agreement between the EU and the United Kingdom currently on the table," said Detlef Seif, the deputy spokesman on European policy for Merkel's CDU/CSU parliamentary group.
May hopes to obtain "reassurances" from Europe over arrangements relating to the Irish border, the main sticking point for British MPs. She was forced to postpone a parliamentary vote on the deal on Monday when it became clear she would suffer a humiliating loss that could have finished her premiership.
Speaking after her meeting with Merkel, May appeared to acknowledge there was no chance of reopening negotiations on the Irish backstop, the part of the deal designed to avoid the return of border infrastructure between Northern Ireland and the Republic of Ireland.
"The backstop is a necessary guarantee for the people of Northern Ireland," May said, adding that whatever relationship the UK wants with Europe "there will be a backstop in it."
May said she wanted to seek assurances from European leaders that the backstop would be a last resort, and if it were to be invoked, it would be temporary.
Earlier, May met with Dutch Prime Minister Mark Rutte at The Hague before flying to Berlin to meet with Merkel and then again to Brussels to see European Council President Donald Tusk.
May also spoke with Austrian Chancellor Sebastian Kurz over the phone. A statement from a spokesperson from the Austrian chancellery said Kurz was in favor "of considering to what extent the British side could be given more security without unraveling the withdrawal agreement."
The statement added: "It is clear that the EU continues to stand by Ireland's side and supports an open border between Ireland and Northern Ireland, especially as it is concerned with the preservation of the Good Friday Agreement (the Northern Ireland peace agreement)."
Afterward, May met with European Commission President Jean-Claude Juncker. She will also visit Irish Premier Leo Varadkar in Dublin on Wednesday.
Juncker said earlier Tuesday that "there is no room whatsoever for renegotiation" on the withdrawal agreement reached between the UK and EU. He added that "the best deal we have achieved is the best deal and the only deal possible."
As she flitted around Europe, rumors swirled at Westminster that members of May's Conservative Party were close to triggering a vote of no-confidence in her leadership. May refused to address the issue when asked about it by a reporter, saying she was focused on delivering her deal.
May is determined to avoid a no-deal outcome: where the UK leaves the EU without transitional arrangements in place. Businesses have warned it could lead to food shortages, grounded flights and a prolonged economic slump.
The British pound plunged 1.6% against the US dollar on Monday, its lowest level in two years, amid fears of a potential no-deal Brexit.
If a deal cannot be reached in time, the EU and the UK could agree to extend the March 29 deadline for Britain to leave the bloc.
The deadlock has led to growing calls for a second referendum. Those calls were buoyed by a decision Monday by the European Court of Justice that the UK can unilaterally revoke Article 50 -- its notification that it plans to leave the EU -- should it so wish.
The Labour Party has indicated it could campaign for a second referendum if May's bill fails and a general election is not called by her or Parliament.
Labour leader Jeremy Corbyn savaged May's government in Parliament on Monday, saying it had "lost control of events and is in complete disarray."
"It's been evident for weeks that the Prime Minister's deal did not have confidence of this House yet she plowed on regardless, reiterating 'this is the only deal available'," Corbyn said.
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