Major U.S. and European banks should be prosecuted for “committing war crimes” over their financing of trade with the Russian regime, according to a top aide to Ukraine president Volodymyr Zelenskyy.

Oleg Ustenko, economic advisor to Zelenskyy, said the Ukrainian government believes banks, such as JPMorgan, HSBC and Citi, are aiding the Kremlin’s war efforts in Ukraine through financing companies that trade oil with Russia. 

“Everybody who is financing these war criminals, who are doing these terrible things in Ukraine, are also committing war crimes in our logic,” he told CNBC’s Hadley Gamble Tuesday on “Capital Connection.”

JPMorgan, HSBC and Citi did not immediately respond to CNBC’s request for comment on those allegations.

Asked directly if he wants to see these banks prosecuted for war crimes, Ustenko said: “Exactly.”

Ustenko said Zelenskyy believes these banks should be held accountable for prolonging the conflict and the war on Ukraine.

His comments came in response to a FT report last week, which said that Ukraine’s government wrote to the chiefs of U.S. and European banks — such as Jamie Dimon from JPMorgan and Noel Quinn from HSBC — urging them to cut ties with the groups that are trading Russian oil.

In letters seen by the FT,  Ustenko wrote to the bankers asking them to cut off financing for businesses that trade Russian oil and sell shares to Gazprom and Rosneft, two of Russia’s state-backed oil and gas companies.

According to the FT, the letters accused Citigroup and Credit Agricole of “prolonging” the war by providing finances to companies that ship Russian oil. The letters also reportedly warned the banks will not be allowed to take part in the reconstruction of Ukraine when the war is over.

CNBC did not immediately hear back from Credit Agricole when asked about those allegations.

Ukraine’s government is gathering all the evidence to send it to the International Criminal Court, Ustenko told CNBC.

“We are collecting all these information” in terms of companies that are financing Russia, he said. “Our Ministry of Justice and our security service of Ukraine are collecting. And then later, this is going to be passed to the ICC,” he added.

This isn’t the first time that Ukraine has gone after Western companies for having business dealings with Russia.

In March, the government was highly critical of big oil companies for still doing business with Russia, and warned that some of those firms could find themselves on the wrong side of history.

Ustenko said the war has taken a significant toll on Ukraine’s economy since Russia’s invasion began on Feb. 24.

“Currently, we are expecting that the Ukrainian economy is going to show a decline on the level of around 35-40%, which is a huge decline,” he said.

He said the decline was because nearly 50% of the businesses “are not operational now or not able to operate at full capacity.”

“When the economy is declining, then the budget revenues are decreased. Again the reason for that is the Russian invasion,” he added.