Ukrainian authorities raided an influential billionaire’s home on Wednesday, part of what President Volodymyr Zelenskiy said was a drive to root out corruption and help the country meet Western standards of clean governance.

Separate raids were carried out at the Tax Office and on the home of a former interior minister, two days before Kyiv hosts a summit with the European Union where it wants to show it is cracking down after years of chronic corruption.

Ukraine sees the summit as key to hopes of one day joining the bloc, a goal that has grown more urgent following Russia’s invasion, and has also embarked on a political shake-up in which over a dozen officials quit or were sacked.

Zelenskiy pledged further action to ensure clean operations of state, citing, in particular, the defence ministry.

“Unfortunately, there are some sectors where the only way to guarantee lawfulness is changing top officials along with institutional change,” he said in a video address.

“There will be as many changes as is necessary so that at last people will not end up getting dirty in their positions.”

Security officials searched the home of businessman Ihor Kolomoiskiy, a one-time Zelenskiy ally, in what several media outlets said was a probe into possible financial crimes.

Kolomoiskiy could not immediately be reached for comment. He has previously denied any wrongdoing.

The Security Service of Ukraine (SBU) later said it had uncovered a scheme to embezzle more than $1 billion at oil producer Ukrnafta and oil refining company Ukrtatnafta, companies that Kolomoiskiy used to partly own.

Photographs circulating on social media appeared to show Kolomoiskiy looking on in the presence of at least one SBU officer inside a wooden home. Reuters could not immediately verify the authenticity of the images.

David Arakhamia, a member of Zelenskiy’s Servant of the People party, confirmed the search of Kolomoiskiy’s home as well as separate raids at the Tax Office and the home of Arsen Avakov, a former interior minister.

Arakhamia said the entire management of the Customs Service was set to be dismissed and that senior defence ministry officials had been served with notices informing them they were suspects in a case.

“The country will change during the war. If someone is not ready for change, then the state itself will come and help them change,” Arakhamia wrote on Telegram.

The Prosecutor General’s Office said in a statement “corruption in a time of war is looting” and four senior current and former officials had been served “notices of suspicion”, along with Ukrtatnafta’s senior management.

The head of the State Bureau of Investigation said the law enforcement action was “only the beginning”.

Zelenskiy presided over the first major political shake-up of the war last week after an outcry over a corruption scandal involving an army food contract.

He was elected in 2019 on an anti-corruption ticket and in late 2021 launched a crackdown on wealthy businessmen known as “oligarchs” who wield influence.