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.