A Ukrainian court ordered tycoon Ihor Kolomoisky to be held in custody for two months on suspicion of fraud and money laundering on Saturday, a striking move against one of the country's most powerful businessmen, Reuters writes.

The detention of Kolomoisky, who is under U.S. sanctions and is a one-time supporter of President Volodymyr Zelensky whose election he backed in 2019, comes as Kyiv is trying to signal progress during a wartime crackdown on corruption.

Defense lawyers said Kolomoisky [among others, majority owner of 1+1 Media] would appeal the ruling, questioning its legality, but that he would not post bail of almost US$14 million in order to secure his release, Radio Liberty reported.

After a hearing at a district court in Kyiv late on Saturday, Kolomoisky, one of Ukraine's richest men, was shown being led away in a blue tracksuit jacket in television footage. He could not be reached for comment.

The Security Service of Ukraine announced the case against Kolomoisky on Saturday morning, publishing photographs on Telegram Messenger showing him being served documents by security officers and signing them.

"It was established that during 2013-2020, Ihor Kolomoisky legalized more than half a billion hryvnias (US$14 million) by withdrawing them abroad and using the infrastructure of banks under (his) control," the agency said in a statement.

After the ruling, Zelensky appeared to allude obliquely to the case in his evening address, thanking law enforcement agencies for showing resolve in bringing long-running cases to justice.

"Without a doubt, there will be no more decades-long 'business as usual' for those who plundered Ukraine and put themselves above the law and any rules... The law must work," he said.

Kolomoisky is seen as one of the class of oligarchs who amassed huge industrial wealth after the 1991 collapse of the Soviet Union and wielded outsize political and economic influence.

Before Russia's February 2022 invasion, Zelensky and his team passed legislation requiring oligarchs to register and to stay out of politics. The war has eroded the oligarchs' power as industrial assets have been destroyed in the east and south, and their television channels have been broadcasting under a centralized signal.

Before winning the presidency, Zelensky rose to prominence as a comedian and played the role of president on a show aired on a Kolomoisky-owned TV channel. He denies Kolomoisky has had any influence over the government.

During the war, Zelensky has emphasized Ukraine's crackdown on corruption as Kyiv has applied to join the European Union and hopes to secure tens of billions of dollars to help rebuild the country after a war which has no end in sight.

Kolomoisky's detention is not the first wartime move involving him.

Last November, the state took control of stakes in major strategic companies, some of which were associated with the businessman, invoking wartime laws to help the war effort.

Earlier this year, security officials searched Kolomoisky's home in connection with a separate investigation into embezzlement and tax evasion at the country's two largest oil companies partially owned by him.

Kolomoisky is a former owner of leading Ukrainian bank PrivatBank, which was nationalized in late 2016 as part of a clean-up of the banking system.

He has owned assets in the energy, banking, and other sectors, including an influential television channel.

The United States imposed sanctions on Kolomoisky in 2021 "due to his involvement in significant corruption". U.S. authorities have also alleged Kolomoisky and a business partner laundered stolen funds through the United States. Kolomoisky has denied any wrongdoing.