TEHRAN, Iran (AP) — Iran’s official news agency is reporting that the head of Bank Melli Iran has resigned over a $2.6 billion fraud case described as the nation’s biggest financial scam.

Tuesday’s report on the IRNA news agency says Mahmoud Reza Khavari explained in his resignation letter that his bank was partly involved in the fraud, though most of the wrongdoing occurred at another bank.

The report says Iran’s finance minister, Shamseddin Hosseini, has accepted the resignation and dismissed a member of the bank’s board.

High-profile resignations are rare in Iran.

Officials say the fraud involved the use of forged documents to get credit at one of Iran’s top financial institutions to purchase assets including major state-owned companies.

Authorities have arrested 22 suspects.