Theresa May will meet top EU official Donald Tusk on Thursday, 24 hours before a major speech on British relations with the bloc after Brexit.
Her talks with the European Council president come amid tensions over the EU’s draft withdrawal treaty.
Mrs May has said the EU’s proposals on Northern Ireland threaten the UK’s constitutional integrity.
The EU says the UK needs to come up a workable alternative to their proposals – which it describes as a “backstop”.
Mrs May, due to chair a meeting of the cabinet before her talks with Mr Tusk, has already pledged not to accept the draft treaty as it stands.
The treaty proposes a “common regulatory area” after Brexit on the island of Ireland – in effect keeping Northern Ireland in a customs union – if no other solution is found.
Both the EU and the Irish government say it is up to the UK to come up with concrete alternatives to what they describe as a “backstop”