A Kyiv court has ordered a two-month detention for billionaire Igor Kolomoisky, under suspicion of fraud and money laundering, Ukrainian media reported late on Saturday.
The arrest of the tycoon - one of Ukraine's richest men and once an ally of President Volodymyr Zelensky - comes as Kyiv says it is still determined to crack down on corruption during the Russian invasion.
"The court chose a preventive measure for Igor Kolomoisky in the form of detention for two months with an alternative in the form of a bail of more than 509 million Ukrainian hryvnias (€12.7 million)," Radio Svoboda reported.
Ukraine's SBU security service said Kolomoisky was under suspicion of fraud and illegally obtaining property.
Kolomoisky, 60, appeared at Kyiv's Shevchenkivsky district court late on Saturday, wearing a yellow t-shirt and a blue jumper - the colours of the Ukrainian flag.
Kolomoisky backed Zelensky's candidacy during the 2019 presidential election.
Before becoming president, Zelensky rose to fame as a comedian, acting on a television channel owned by Kolomoisky.
Since Russia invaded in February last year, Zelensky has repeatedly vowed to fight corruption in Ukraine - a key requirement by Kyiv's western allies.