French Interior Minister Gerald Darmanin said on Thursday that he had clearly told his British counterpart Priti Patel that the United Kingdom must stick to its commitments on migrants trying to cross the Channel to reach Britain.
Darmanin was responding after Britain approved plans to turn away boats illegally carrying migrants to its shores, deepening a rift over how to deal with a surge of people risking their lives by trying to cross one of the world's busiest shipping lanes in small dinghies.
"France will not accept any practice that goes against maritime law, and will not accept any financial blackmail," Darmanin tweeted.
Hundreds of small boats have attempted the journey from France to England this year, across one of the world's busiest shipping lanes.
Border officials will be trained to force boats away from British waters but will deploy the new tactic only when they deem it safe, a British government official who asked not to be named said on Thursday.
Patel has told French Interior Minister Gerald Darmanin that stopping people making their way from France on small boats was her "number one priority."