The bank urged all state institutions to work together to protect financial stability and to take legal action against all those spreading "untrue and ill-intentioned rumours" about the health of banks.

"In recent days there has been an attempt to destabilise the state through an organised attack against Bulgarian banks without any reason," the statement said, adding that First Investment Bank (>> First Investment Bank AD Sofia) had been a major target.

Last week, customers unnerved by reports of shady deals involving Corporate Commercial Bank (Corpbank) (>> Korporativna targovska banka AD Sofia) rushed to withdraw their deposits, prompting the central bank to seize control of the lender and shut down its operations.

(Reporting by Angel Krasimirov, Tsvetelia Tsolova and Matthias Williams; Writing by Gareth Jones)