The foreigners released included Aslin, Pinner and a Moroccan who had all been sentenced to death in June after being captured fighting for Ukraine. Also freed were three other Britons, two Americans, a Croatian, and a Swedish national.

The timing and magnitude of the swap came as a surprise, given Russian President Vladimir Putin had announced a partial troop mobilization earlier in the day in an apparent escalation of the conflict that began in February. Pro-Russian separatists had also said last month that the Mariupol commanders would go on trial.

President Volodymyr Zelenskiy said the swap - which involved help from Turkey and Saudi Arabia - had been under preparation for quite a long time and involved intense haggling. Under the terms of the deal, 215 Ukrainians - most of whom were captured after the fall of Mariupol - were released.

In exchange, Ukraine sent back 55 Russians and pro-Moscow Ukrainians and Viktor Medvedchuk, the leader of a banned pro-Russian party who was facing treason charges.