(Bloomberg) -- French Prime Minister Jean Castex asked the U.K. to do more to deter migrants from crossing the Channel, in a letter to Boris Johnson.

The letter sent on Wednesday evening should be seen an invitation to start a constructive discussion that includes the European Union, and not a blame game, an official in Castex’s office said, asking not to be identified to comply with government rules. France hasn’t received a response from the U.K. just yet.

Castex renewed previous calls for the U.K. to make itself less attractive to illegal migrants and put more checks on black market work. He also asked Johnson’s government to share more intelligence and open legal options for migrants when possible, including for those trying to join family members in the U.K., the official said.

The disclosure of the letter’s contents is somewhat ironic given French government officials were upset when Johnson published on Twitter his own letter to Macron last week. In it, he urged France to take migrants back. Castex’s office described that proposal as not serious and irresponsible.

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The official said the priority is to coordinate with European partners on migration -- a particularly sensitive topic in France, where it’s a main theme of campaigns for the April presidential election. And in the U.K. where Johnson pitched tighter border controls as a benefit of Brexit. EU interior ministers are meeting on Dec. 9 to discuss the issue.

Castex’ office wasn’t immediately able to say if the U.K. had started transferring the 62.7 million euros it agreed to give to France in July to fight human trafficking on French coasts in 2021-2022.

The personal tensions between Emmanuel Macron and Johnson, meanwhile, were highlighted in a new report by French newspaper Canard Enchaine. During a trip to Zagreb last week -- and just after 27 people were reported to have died trying to reach the U.K. -- the French president called Johnson a “clown” and a “good-for-nothing,” according to the paper.

“Bojo talks to me, he’s down to earth, everything’s fine, we’re having grown-up discussions and then he sticks it to us either beforehand or afterwards in an inelegant manner,” Macron was quoted by the Canard as saying. “It’s always the same circus.”

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