President Trump's peace plan became public last month, sparking alarm that it was too favorable to Moscow. It was revised following talks in Geneva between the U.S. and Ukraine a week ago.

Ukrainian naval drones hit two oil tankers from Russia's so-called "shadow fleet" as they travelled through the Black Sea, Ukrainian officials have said. Footage verified by the BBC shows waterborne drones speeding through the waves into the vessels, before detonating into a ball of flame, sending black smoke into the air.