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," 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.