A close political associate of Ukrainian multibillionaire Igor Kolomoyski was arrested Saturday as part of a crackdown on corruption and organised crime, authorities said.
Guennadi Korban, 45, a candidate for the mayoralty of Kiev and close to Kolomoyski, a former governor of the eastern region of Dnipropetrovsk, "was arrested along with other suspects," a statement by the SBU security services read.
The arrests came on a day which saw a protest near the presidential palace against President Petro Poroshenko, lambasted by some sections of the public as failing to deliver on a promise to crack down on corruption.
Around 100 lawmakers attended the protest where participants waved aloft banners reading "Poroshenko covers up corruption".
Saturday's arrests came as part of a sweep in several regions into activities including the "organisation of a criminal group," along with "theft and misappropriation" of funds.
One incident under investigation covers the reported theft of 40 million hryvnias (1.5 millions euros, $1.7 million) officially "earmarked for Ukrainian soldiers" fighting pro-Russian separatists in the east of the country, the SBU said.
Korban's Ukrop party blasted what it termed "political repression" targeting "patriots."
Following news of Korban's detention, Kolomoyski's 2+2 television station flashed up rolling "freedom for Korban" messages.
Kolomoyski, Ukraine's second richest man managed in a brief spell as governor of Dnipropetrovsk to keep a lid on separatist tension in eastern Ukraine.
But Poroshenko had him dismissed last year after the oligarch who has major banking and energy interests was accused of setting up his own militia and trying to hold on to a state-affiliated oil company.
Poroshenko, himself a successful businessman who has not sold his firms despite electoral promises to divest them, has promised to crack down on oligarchs.
He furthermore warned state governors against creating their own "pocket armies."
Saturday's events came a day after an annual wealth list showed the value of Poroshenko's assets soared despite economic crisis and conflict while those of other tycoons shrank.
The 50-year-old Western-backed president's business empire ranges from chocolates to media holdings still under his control and he ranks as his country's sixth-richest man after his assets reportedly rose by 20 percent to $979 million (889 million euros) -- only just supporting his claim he is no longer a billionaire.
One demonstrator, Vitali Selyk, 26, said he was fed up with state corruption.
Waving a banner wqhich read "new president, same old corrupt officials", he said: "I am outraged that nothing is done against corruption. My businesssmen friends say there is more corruption now with the new regime" of Poroshenko, who took office last year.