Ukrainian President Volodymyr Zelenskyy has proposed swapping detained pro-Russian Ukrainian politician and oligarch Viktor Medvedchuk for captured prisoners of war.
Earlier today, Ukrainian officials said the fugitive Mr Medvedchuk, who is both a pro-Russian opposition leader and a close associate of Russian leader Vladimir Putin, was detained in a special operation carried out by the country's secret service.
Mr Zelenskyy proposed swapping Mr Medvedchuk for captured Ukrainian service personnel in a video address today.
"I propose to the Russian Federation to exchange 'your guy' for our boys and our girls who are now in Russian captivity. It is therefore important that our law enforcement and military also consider this possibility," Mr Zelenskyy said.
He also warned Russia that Ukrainian forces would capture more soldiers.
"We will establish the full truth about all these savages. No matter how much time and effort it takes, we will find them all. Let Medvedchuk be an example for you," Mr Zelenskyy said.
"Even the former oligarch did not escape. What to say about much ordinary criminals from the Russian middle of nowhere. We will get everyone."
Earlier, Ivan Bakanov, the head of Ukraine's national security agency, said on the agency's Telegram channel that Mr Medvedchuk had been arrested.
The statement came shortly after Mr Zelenskyy posted on social media a photo of Mr Medvedchuk sitting in handcuffs and wearing a camouflage uniform with a Ukrainian flag patch.
The Ukrainian president said he had been captured during a "special operation".
"A special operation was carried out thanks to the SBU," Mr Zelenskyy wrote in Russian on his verified account on the social media platform Telegram, referencing Ukraine's Security Service.
Mr Medvedchuk leads the pro-Russian party Opposition Platform - For Life.
He was being held under house arrest before the war began and disappeared shortly after hostilities broke out on February 24.
Mr Putin is the godfather to Mr Medvedchuk's youngest daughter.
Last year, Ukrainian authorities opened a treason case against Mr Medvedchuk.
He denies wrongdoing.
Some experts have speculated that if Mr Putin had planned to install a puppet leader after toppling Ukraine's government, Mr Medvedchuk would be a candidate.
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- Reported with Reuters, Associated Press, CNN