Ukraine on Monday aired a video showing Viktor Medvedchuk, a detained pro-Russia tycoon and ally of President Vladimir Putin, seeking to be exchanged in return for an evacuation of civilians and troops from the besieged port city of Mariupol.

Mariupol has become a symbol of Ukraine's unexpectedly fierce resistance since Russian troops invaded the former Soviet state and pro-democratic country on February 24.

"I want to ask Russian President Vladimir Putin and Ukrainian President Volodymyr Zelensky to exchange me for Ukrainian defenders and residents of Mariupol," he said in the video published by Kyiv's security services, wearing black clothes and looking directly into the camera.

Medvedchuk, who escaped from house arrest after Russia's invasion and was detained last week, said the troops and residents there "do not have the possibility of a safe exit through humanitarian corridors".

Medvedchuk is one of Ukraine's richest people and is known for his close ties to Putin. He is also a politician.

Medvedchuk is known for his close ties to Russian President Vladimir Putin
Medvedchuk is known for his close ties to Russian President Vladimir Putin AFP / Sergei SUPINSKY

He says Putin is the godfather to his youngest daughter, Darya.

The Kremlin had earlier rejected the idea of exchanging him for Ukrainians detained by Russia, and Zelensky floated the idea of a swap.

"He is a foreign politician," Putin's spokesman Dmitry Peskov, explained last week.

Separately on Monday Russian state TV broadcast a video Monday of what it described as "Britons" captured fighting for Ukraine demanding that Prime Minister Boris Johnson negotiate their release.

The two men shown in the video asked to be exchanged for Medvedchuk, who had been accused of treason and attempting to steal natural resources from Russia-annexed Crimea and of handing Ukrainian military secrets to Moscow.