French Foreign Minister Jean-Yves Le Drian told his British counterpart Dominic Raab that a breach by Britain of the withdrawal agreement reached with the European Union would be "unacceptable", his spokeswoman said on Thursday.
Le Drian spoke to Raab on the sidelines of an E3 meeting in London to discuss Iran on Thursday.
The European Union was on Thursday exploring possible legal action against Britain over Prime Minister Boris Johnson's plan to undercut parts of the Brexit divorce treaty, with EU officials saying London may already be in breach of the treaty.