Federal prosecutors are examining whether Binance failed to stop trading that breached U.S. sanctions on Iran, Bloomberg reported on Monday, citing people familiar with the matter.

The Manhattan U.S. attorney's office is handling the inquiry, and the Justice Department's criminal division in Washington is also involved, according to the report. Authorities are scrutinizing whether the exchange knowingly allowed the Iran-linked trading to take place on its platform.

The specific transactions under examination were not clear. Justice Department investigations can close without charges being filed. Spokespeople for the Justice Department and the Manhattan U.S. attorney's office declined to comment.

"We maintain a zero-tolerance policy for sanctions violations," Binance said in a statement, adding that it cooperates with law enforcement and is "committed to rooting out and shutting down bad actors."

The probe comes almost three years after the exchange pleaded guilty to failing to comply with U.S. banking and sanctions law, paid $4.3 billion and accepted two corporate monitors. Co-founder Changpeng Zhao stepped down as chief executive, served four months in prison and was pardoned by President Donald Trump last year.

The investigation follows months of reporting on alleged Iran-linked flows through the platform. Fortune reported on February 13 that internal investigators had found more than $1 billion moving through the platform to Iran-linked entities and were subsequently dismissed. The Wall Street Journal covered the firings on February 23, and the New York Times reported the same day that the sum sent to Iranian entities totaled $1.7 billion. Senator Richard Blumenthal opened a preliminary inquiry the following day, demanding records on two entities, Hexa Whale and Blessed Trust.

Binance rejected that account in a March 10 blog post, saying the funds neither originated nor terminated on its platform, and that at most $126.1 million reached wallets linked to Iran after multiple transaction hops, of which at most $24.1 million reached wallets related to the Islamic Revolutionary Guard Corps (IRGC). The company said the Iranian links surfaced only after it had begun its own investigation, and that no employee was dismissed for escalating compliance concerns. It separately told Blumenthal that its compliance process had been effective, and has sued The Wall Street Journal over the reporting.

Both entities flagged by Blumenthal resurfaced last week, when Manhattan prosecutors sought the forfeiture of $61 million they say came from Iranian black-market oil sales and was laundered through Binance. According to prosecutors, two Hong Kong-registered companies misrepresented their business activities. Binance was not accused of wrongdoing in that action.

The inquiry comes amid a broader sanctions campaign. The Office of Foreign Assets Control (OFAC) gave itself the power in August to designate any foreign person operating in Iran's digital asset sector, regardless of where they are based—one of five sectoral determinations issued under what Treasury calls Operation Economic Outcast. Washington sanctioned firms and individuals it says finance Hezbollah and other Iranian proxies on September 10.