Ukraine arrested the oligarch who owns the TV station that aired Volodymyr Zelenskyy's show before he became president

Ukraine has detained one of its most prominent billionaires whose relationship with President Volodymyr Zelenskyy has previously raised eyebrows.

The country's security service said on its Telegram channel that oligarch Ihor Kolomoisky would be held in custody for two months on fraud and money laundering charges.

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

Pictures shared alongside the statement show Kolomoisky, who Forbes estimates is worth $1 billion, being served with notices at his home by Ukrainian officers. He appeared in court on Saturday.

Ukrainian oligarch Ihor Kolomoisky appeared in court on Saturday. Vladyslav Musiienko/Reuters

Zelensky said in his nightly TV address Saturday it would not be "business as usual for those who plundered Ukraine and put themselves above the law. Each of us feels that this will be a Ukraine with different rules," outlets including BBC News reported.

Zelenskyy was elected presidency in 2019 on an anti-corruption platform intended to address an endemic problem in Ukraine.

A survey published last month by the Kyiv International Institute of Sociology found that 89% of Ukrainians thought corruption was the country's most serious problem after its war with Russia.

According to Transparency International's latest Global Corruption Barometer, 38% of households said they'd paid bribes to public servants.

While the arraignment of Kolomoisky will be intended to signal the latest clampdown on corruption, Zelenskyy's own relationship with the media mogul has come under scrutiny.

The oligarch returned to Ukraine from self-imposed exile weeks after Zelenskyy was elected. He fled after being accused by the previous president, Petro Poroshenko, of diverting millions of dollars from a bank he controlled to other companies in his empire, forcing a bailout.

Kolomoisky owns the TV station 1+1 that broadcast "Servant of the People," in which Zelenskyy played a comedian who becomes president. Zelenskyy rejected suggestions he may be beholden to Kolomoisky at the time, but his arrest still comes as a surprise.

Justice minister Denys Maliuska said Ukraine also planned to extradite corrupt officials who had fled abroad.