As he considered a run for President of Ukraine, Volodymyr Zelensky, a former comedian, joked about the country's rampant high-level corruption.

"Is it possible to become President and not steal?" Zelensky quipped. "It's a rhetorical question, as no one has tried so far."

Zelensky’s promises to fight corruption propelled him to the presidency in 2019 and underpinned his politics before Russia’s full-scale invasion of Ukraine in 2022. But now a sweeping corruption investigation that has reached his inner circle is threatening his support both at home and abroad, and tarnishing his image as a lionised wartime leader.

Ukrainian investigators say that a criminal organisation led by a business partner of Zelensky siphoned off and then laundered $100 million from the country's publicly owned nuclear power company and engaged in other fraud and financial crimes.

Two government ministers in the case submitted letters of resignation after Zelensky asked them to step down, and the Prime Minister that he appointed has requested that sanctions be imposed on the business partner, Timur Mindich. Investigators say that Mindich, who is an owner of a comedic television studio founded by Zelensky, fled Ukraine in the predawn hours of Monday before a search of his home.

Throughout the week, the independent agency leading the investigation, the National Anti-Corruption Bureau of Ukraine, has drip-fed new revelations of corruption by posting recordings from wiretaps online. Its slow unfurling of the case, including slickly produced videos featuring its detectives, has gripped Ukrainians while gradually ratcheting up pressure on Zelensky without revealing how high the inquiry will reach.

Zelensky has not been directly implicated. He said in a speech on Wednesday that he supported "every investigation carried out by law enforcement and anticorruption officials".

But the revelations touch a particular political vulnerability for Zelensky. This summer, he moved to curtail the independence of the anticorruption investigators as they pursued the case. He reversed course after Ukrainians poured into the streets in the country's first large protests during the war, saying that Zelensky was threatening Ukraine's fragile democracy.

To many Ukrainians, the allegations of corruption at the nuclear power giant are especially galling as millions suffer through rolling daily blackouts because of Russian attacks. On Friday, Russia launched 430 drones and 18 missiles in a volley concentrating on the capital, Kyiv, killing four people and wounding dozens of others.

The same company that is trying to keep the lights on as winter approaches is now linked to a scheme to enrich Mindich, who has been described by the political Opposition and the news media as having had broad political influence over Zelensky.

The revelations are a remarkable reversal for Zelensky. He had once cultivated an image as a leader who would open up Ukraine's politics by sweeping away the wealthy insiders known as oligarchs. Now, nearly seven years since the last election, and with a new one nowhere in sight because of the war, many Ukrainians see him as operating within a small, closed circle, unbound by the rules.

"I can only assume he is thinking that he does a lot to fight the Russians, and nobody has a right to say anything to him, even Ukrainian anticorruption institutions," said Olena Scherban, a lawyer who represents an investigator in the case who was arrested by intelligence officials who report to Zelensky.

Zelensky has responded to the revelations by condemning any fraud that might have occurred and calling for the prosecution of those accused of committing crimes. And he has signalled a break in ties with the implicated officials — including Herman Halushchenko, the justice minister, and Svitlana Hrynchuk, the energy minister — as well as with Mindich.

Mindich has not publicly commented on the case, and efforts by The New York Times to reach him through Zelensky's production studio, Kvartal 95, were unsuccessful.

Ukraine's main Opposition party, European Solidarity, has called for a no-confidence vote on Zelensky's cabinet of ministers. The vote's prospects are unclear as Zelensky's party holds a majority in Parliament.

New York Times News Service