The crisis in Kuwait’s banking sector deepened on Tuesday as the chairman of Gulf Bank resigned over derivatives losses and Moody’s warned it could downgrade the bank, the country’s second biggest lender.

Kutayba Al Ghanim replaced his brother Bassam Al Ghanim as chairman of Gulf Bank after depositors on Monday started to withdraw deposits from the stricken bank. It was the first known bank run in the region during the crisis and came despite the Kuwaiti central bank’s pledge to support the bank and guarantee all bank deposits in the country.