Prime Minister Theresa May will meet EU leader Donald Tusk on Sunday ahead of a summit with Arab leaders, officials said, but should not expect a Brexit breakthrough.
The British leader will sit down with Tusk, president of the European Council, in the Egyptian resort of Sharm el-Sheikh ahead of the European Union talks with the Arab League.
Tusk represents the governments of EU member states, and holds the key to any progress in May's effort to lobby Brussels to renegotiate the terms of Britain's departure from the bloc.
He did not meet May when she was in Brussels earlier the week for talks with EU Commission president Jean-Claude Juncker, and officials here do not expect a breakthrough when he sees her at 4:30pm on Sunday.
"There will be no deal in the desert in Sharm el-Sheikh, this is a summit between the EU and the Arab states," an EU source told reporters in Brussels.
Another official said: "It's an opportunity where everyone can talk, but don't expect a deal there."
Only 24 of the 28 EU leaders have confirmed they will attend the Red Sea summit, and all would have to be present to agree any new or modified Brexit deal.
Nevertheless, May is expected to meet some of her counterparts one-on-one on the sidelines of the meeting to push her case for changes to the divorce agreement.
This could pave the way towards a later breakthrough, perhaps at the next planned full EU summit on March 21 and 22, just a week before Britain leaves the bloc.
Yesterday, EU negotiator Michel Barnier told France's Europe 1 radio it was time for May to take a decision and present a Brexit plan to her parliament.
"We don't need extra time, what we need now is a decision and for everyone to take responsibility," he said.
He did not exclude granting Britain more negotiating time, but said it was now up to the British "to take their responsibilities and assume the consequences of decisions they took democratically".
Brussels however is open to adopting a more ambitious political declaration, alongside the legally binding withdrawal treaty that would set a roadmap for negotiating close EU-UK trade ties.
The British government said Thursday that Brexit talks will focus on securing new guarantees to reassure lawmakers, rather than on demanding that a divorce deal already concluded with the EU be reopened.
EU leaders insist the withdrawal agreement, which they struck with Britain last year, cannot be renegotiated to appease British MPs who rejected it in parliament.