Berlin (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.

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