Ukrainian-Israeli-Cypriot businessman and politician Igor Kolomoyskyi
The searches came ahead of a key summit with the EU and appeared to be part of a push by Kyiv to reassure military and financial donors in European capitals and Washington that Ukraine is tackling systemic graft.
Comment: Do they plan to seize their assets?
"We are carrying out the task set by Ukrainian President Volodymyr Zelensky and simultaneously delivering a global blow to the internal enemy," announced Vasyl Maliuk, the head of Ukraine's security service, the SBU.
"Every criminal who has the audacity to harm Ukraine, especially in the conditions of war, must clearly understand that we will put handcuffs on him."
The searches have targeted influential billionaire Igor Kolomoisky and former interior minister Arsen Avakov, said the head of Zelensky's party David Arakhamia.
Comment: Kolomoisky who funded Zelensky's rise to power? Zelensky is Not in Charge of Ukraine, Nazis Are - And They Believe They Are on a Mission From God to 'Derussify Ukraine in Holy War'
In 2019, Kolomoisky emerged as the top backer of Zelensky's presidential bid. Though Zelensky made anti-corruption the signature issue of his campaign, the Pandora Papers exposed him and members of his inner circle stashing large payments from Kolomoisky in a shadowy web of offshore accounts.
Law enforcement also raided tax offices in the capital and senior customs officials were fired, Arakhamia said.
Ukraine has suffered from corruption for years but efforts to stamp it out have been overshadowed by Moscow's invasion last February.
Comment: Ukraine has repeatedly featured as one of Europe's top most corrupt countries, which likely made it much easier for the West to use it to wage its proxy war.
Ukraine's latest push to clean up its image is aimed at appeasing Western backers.
In the biggest political shakeup since the launch of Moscow's assault on Ukraine, authorities last week fired around a dozen senior figures, including defence officials and a top aide to the president's office.
Comment: Most were fired over fraud and embezzlement - which isn't unusual in Ukrainian politics - however one, Arestovych, quit after saying that Ukraine had no chance of winning the West's war: Arestovych resigns from the post of advisor to Ukraine's presidential office
Wednesday's raids came two days before Zelensky was expected to host a summit with the European Union, which has urged reforms to facilitate deeper integration.
Investigators from the SBU released images of a search from the home of Kolomoisky, who was barred from entering the United States over allegations of corruption and undermining democracy.
'All necessary steps'
Prior to the invasion, Kolomoisky was one of the country's richest men with holdings in a slew of industries, including media, aviation and energy.
The security service said the search had been launched over an investigation into the embezzlement of 40 billion hryvnia (more than $1 billion) from energy holdings.
The government seized stakes in the energy companies -- oil producer Ukrnafta and refiner Ukrtatnafta -- as part of moves to consolidate the war effort.
Comment: Those stakes might help fund the war effort.
The SBU also said it had uncovered a scheme by the head of the Kyiv tax office involving "multimillion-dollar" fraud schemes. They accuse the official of having abused a position of authority.
On Tuesday, Zelensky vowed officials would take further measures to sweep away graft.
"People in the government who do not meet the basic requirements of the state and society should not occupy their seats," he said.
The State Bureau of Investigation and the Prosecutor General's Office said Wednesday they had informed several senior officials they were under investigation for crimes including misappropriation of state funds and misuse of state property.
Last week, the defence ministry announced the resignation of deputy minister Vyacheslav Shapovalov, who worked on logistical support for the army. The ministry has been accused of signing food contracts at prices up to three times the market rates.
Donetsk battle getting 'worse'
Zelensky is now working to drum up political backing for Ukraine at a critical time in the conflict, with Russian forces claiming to have captured fresh ground in the eastern Donetsk region.
AFP journalists near the small town of Vugledar in the battle-scarred industrial region this week witnessed artillery barrages to keep Russian forces at bay.
"The more time passes, the worse the situation gets," Oleksandr, 45, said from a trench just five kilometres (three miles) from Vugledar.
Ukrainian Foreign Minister Dmytro Kuleba said Tuesday that a dozen countries had promised more than 100 tanks after Germany and the United States signed off on the deliveries last week.
Now Zelensky and other Ukrainian officials are calling on the West to supply fighter jets and long-range artillery too.
The Kremlin said Wednesday that any deliveries of long-range weapons to Ukraine would not alter Russia's military objectives in the pro-Western country or change fighting on the battlefield.
"It would require greater efforts from us. But again, it won't change the course of events," Kremlin spokesman Dmitry Peskov told journalists.
In Geneva, two UN rights experts on Wednesday backed the International Olympic Committee's moves towards letting Russians compete in the Paris 2024 Games, a prospect that has already brought threats of a boycott from Ukraine.
The experts, Alexandra Xanthaki and Ashwini K.P., additionally urged the IOC to lift the ban on athletes who actively support Russia's war in Ukraine.
Comment: Other than the psychopaths eating their own, for more insight into just what might be going on, see: The Kiev Purge: What has spurred a wave of resignations among senior Ukrainian officials?