Ukrainian lawmaker Viktor Medvedchuk has been charged with three counts of treason by Kyiv authorities.
A top Ukrainian official did not exclude the possibility of a prisoner swap with Russia if a Kyiv court convicts a Kremlin-leaning politician of treason.
Oleksiy Danilov, the secretary of the National Security and Defense Council, said in a TV interview that Kyiv would "gladly" hand over lawmaker Viktor Medvedchuk to Moscow in exchange for Ukrainians held in Russian prisons if the opportunity arises.
However, he said such a decision can only be made by President Volodymyr Zelenskiy.
Ukrainian Prosecutor-General Iryna Venediktova on May 11 charged Medvedchuk, the leading figure in the Opposition Platform — For Life party, with three counts of treason.
A Kyiv court placed Medvedchuk under house arrest on May 13 and set the start of his trial for July in what could be the highest-profile political case in Ukraine in years.
He denies the charges and calls them politically motivated.
Medvedchuk promotes closer ties with Russia, which annexed Crimea and backed fighters in eastern Ukraine following the overthrow of Kremlin-leaning President Viktor Yanukovych in 2014.
The war in eastern Ukraine, which continues to this day, has killed more than 13,000 people.
Medvedchuk is accused among other things of concealing his ownership of natural gas assets in Russian-occupied Crimea with the help of the Kremlin.
Ukraine in February sanctioned Medvedchuk and three television stations believed to be owned by him.
Ukraine accuses the stations of promoting Russian disinformation.
The 66-year-old Medvedchuk has close ties to Russian President Vladimir Putin, who is the godfather of his daughter.
Medvedchuk has frequently traveled to Moscow to discuss with Russian officials, including Putin, peace in eastern Ukraine, prisoner swaps, as well as natural gas deals.
Putin on May 14 accused Ukraine of carrying out "anti-Russian" policies in a possible reference to the charges against his friend Medvedchuk.
Analysts say that Zelenskiy has grown frustrated with the lack of progress in the peace talks with Russia and sees Medvedchuk as a hindrance.
Zelenskiy, a political novice, came to power in May 2019 in part on a promise to end the war in eastern Ukraine and free political prisoners.
He carried out three prisoner swaps with Russia and the Kremlin-backed fighters in eastern Ukraine within his first year but has made no progress since April 2020.
Russia stills holds about 100 Ukrainians — including many Crimean Tatars — that Kyiv deems to be political prisoners.
Zelenskiy’s ratings have tumbled from above 70 percent in 2019 to below 30 percent this year amid disillusionment with his leadership.