A group of internal investigators at the giant cryptocurrency exchange Binance made a series of startling discoveries last year.

People in Iran had gained access to more than 1,500 accounts on the Binance platform over the previous year. About $1.7 billion had flowed from two Binance accounts to Iranian entities with links to terrorist groups, a possible violation of global sanctions. And one of those accounts belonged to a Binance vendor.

After uncovering the transactions, the investigators reported them to top executives, according to company records and other documents reviewed by The New York Times.

Within weeks, Binance fired or suspended at least four employees involved in the investigation, according to the documents and three people with knowledge of the situation. The company cited issues such as “violations of company protocol” related to the handling of client data.

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By analyzing crypto transactions, Binance investigators found that accounts on the exchange had moved funds to entities tied to Iran, a major foreign adversary that the Trump administration has been preparing to strike. When Binance pleaded guilty three years ago, it agreed to pay a $4.3 billion penalty and admitted that it had violated U.S. sanctions, including by allowing customers from Iran to use its platform. It also agreed to alert U.S. authorities to any lawbreaking detected on the exchange.

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It’s unclear exactly why the investigators were disciplined. Over the last few months, more than half a dozen compliance officials have left Binance, including a sanctions manager and the leader of the enterprise compliance team. Binance’s chief compliance officer, Noah Perlman, has also discussed leaving, a person familiar with the matter said.

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In the middle of last year, Binance’s compliance experts were contacted by law enforcement officials from Israel who wanted to discuss terror financing routes connected to Iran. Binance began an investigation that centered on a now-defunct business called Hexa Whale Trading Limited.

Hexa Whale, based in Hong Kong, had used Binance to send $490 million to crypto wallets tied to Iranian entities, according to the documents. At one point, the documents said, an Israeli official told the investigators that Hexa Whale was financing terrorist organizations such as the Houthis, an Iran-backed militia that controls Yemen’s north.