US authorities have extended investigations of UK's HSBC and Standard Chartered to search for information on Chinese banks' businesses with Iran.
Prosecutors hope that the banks' executives, as part of settlements, will shed more light on Chinese banks' independent relationships with Iran, according to the New York Times.
Both banks have extensive Asia and Middle East networks and both have deep links with China's financial system.
The informal probes involve the US Justice Department and the Manhattan, New York district attorney's office.
But US prosecutors do not yet have enough information to launch formal investigations, it added.
The main concern is that suspect Iran firms may tap Chinese banks to help transfer money to them that could be routed through US units of the Chinese banks.
Investigations into sanctions violations by other major global banks, including ABN-Amro, Barclays, Credit Suisse, Lloyds and ING, "yielded valuable information about Chinese banks' relationships with Iran," the Times said, citing US law enforcement officials.
The US has imposed official sanctions on the Bank of Kunlun, which is controlled by the state-owned energy giant China National Petroleum Corp.
Do you know more about this story? Contact us anonymously through this link.