Ukrainian law enforcement raided tax offices and residences linked to two high-profile figures — an oligarch and a former minister — as part of a wider anti-corruption drive, officials said.
The searches came before US and European officials meet Ukrainian authorities in Kyiv to discuss reconstruction and the need for transparency.
President Volodymyr Zelenskyy’s government has intensified its crackdown on corruption with the most notable casualties being senior government officials who were fired last week.
Searches on Wednesday were focused on influential billionaire Igor Kolomoisky and former interior minister Arsen Avakov, said the head of Mr Zelenskyy's party, David Arakhamia.
“We are carrying out the task set by President Zelenskyy and simultaneously delivering a global blow to the internal enemy,” said Vasyl Maliuk, the head of Ukraine's SBU security service.
“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.”
Law enforcement also raided tax offices in Kyiv and senior customs officials were fired, Mr Arakhamia said.
SBU investigators released images of a search at Mr Kolomoisky’s home.
Before the invasion, he was one of the country's richest men with holdings in industries including media, aviation and energy.
The security service said the search had been launched as part of an investigation into the embezzlement of more than a$1 billion from energy holdings.
The Ukrainian government seized stakes in the energy companies — oil producer Ukrnafta and refiner Ukrtatnafta — as part of moves to consolidate the war effort.
The SBU also said it had uncovered a scheme by the head of the Kyiv tax office over “multimillion-dollar” fraud schemes, accusing the official of abusing a position of authority.
Ukraine has for years suffered endemic corruption and efforts to stamp it out have been overshadowed by Moscow's invasion last February.
Ukraine has now launched a new push, in part to clean up its image to appease western backers.
Authorities last week fired about a dozen senior figures, including defence officials and a top aide to the President's office.
The raids on Wednesday came two days before Mr Zelenskyy was expected to host a summit with the EU, which has urged reforms.