According to the Ukrainian president and parliament, mayor Ivan Fedorov was abducted on Friday by Russian soldiers occupying Melitopol, a city halfway between Mariupol and Kherson, because he "refused to cooperate with the enemy".

On Wednesday a video posted on Telegram showed President Volodymyr Zelensky speaking to him on the phone and telling him he was "happy to hear the voice of a man alive".

Fedorov replies he is "much better".

"Thank you for not abandoning me. I will need one or two days to recover and then I will be at your disposal to contribute to our victory," he says.

Dasha Zarivna, a spokeswoman for the Ukrainian presidency, said on Ukrainian television late Wednesday that Federov was swapped for nine captured Russian soldiers, aged 20 and 21.

"These are basically children, conscripts, who according to the Russian defence ministry are not present in Ukraine," Zarivna said.

"But the whole world sees again that they are there."

The parliament said the mayor was seized while at the city's crisis centre dealing with supply issues.

Zelensky on Saturday called on the leaders of France and Germany to help secure his release.

The mayor of Dniprorudne, another town in southern Ukraine, was also abducted on Sunday, drawing strong condemnation from the European Union.