PARIS (Reuters) - French Prime Minister Jean Castex told his British counterpart, Boris Johnson, that he rejected the idea of a joint British-French patrol in the English Channel to fight illegal migration, a letter obtained by Reuters showed on Thursday.

       "France is ready to pursue our operational cooperation with the United Kingdom", the letter said, but added:

       "We cannot accept (...) that British police or military patrol at our coast. It's a matter of our sovereignty."

       Boris Johnson earlier this month suggested a joint coast patrol in a letter he sent to French President Emmanuel after 27 migrants lost their lives as the tried to reach British shores.

       (Reporting by Tassilo Hummel)