President Volodymyr Zelensky's chief of staff has reported a prisoner swap which saw 35 Ukrainian soldiers and one civilian exchanged for 35 Russian servicemen held in Ukraine.

Andriy Yermak said the Ukrainian prisoners of war included fighters who spent weeks defending the Azovstal steelworks plant in the key south-eastern port city of Mariupol.

After a bloody and destructive battle over the massive steelworks, nearly 1,000 fighters submitted to the Russian side in May after being told to do so by Ukraine's top military leaders.

Last month the BBC's Hugo Bachega spoke to one of the fighters released in an earlier prison swap, Illia Samoilenko, who said they were being kept in inhumane conditions by Russia.

The Russian Ministry of Defence has also confirmed the swap, saying its servicemen would be flown to Moscow to undergo treatment and rehabilitation.