U.K. Prime Minister Keir Starmer and French President Emmanuel Macron announced a deal that aims to address the record number of migrants crossing the English Channel.

At a summit on Thursday, Prime Minister Keir Starmer and President Emmanuel Macron also announced a “one in, one out” pilot program on migrants crossing the English Channel.

Britain and France will join together to use nuclear weapons against any “extreme threats” towards Europe, Sir Keir Starmer and Emmanuel Macron have declared. A newly-signed declaration by the leaders will state that the two countries’ nuclear deterrents are independent but can be co-ordinated in a joint attack on Europe’s enemies.

The UK and France agreed Thursday to form a nuclear deterrent pact to fend off “extreme” threats to the continent in the face of Russian aggression and fears that the US will begin to pull military support under President Trump.