German Chancellor Angela Merkel and French President Emmanuel Macron have demanded that Russia release Ukrainian sailors who were seized along with their ships last month.
Moscow accused the 24 sailors of illegally crossing the Russian border.
Ukraine said Russia captured the two small gunboats and one tugboat illegally and accused Moscow of military aggression.
"We demand safe, free and unimpeded transit for all ships through the Kerch Strait and the immediate and unconditional release of all illegally detained Ukrainian seafarers," Merkel and Macron said in a joint statement on Friday.