Bulgaria's central bank, in an unprecedented statement, warned earlier of a systematic attempt to destabilise the country through attacks on the banking system and it vowed to use all tools at its disposal to protect citizens' savings.

Shares in Bulgarian banks tumbled for a second consecutive day on Friday amid rumours of a possible run on another lender, one week after the central bank stepped in to rescue Corporate Commercial Bank (Corpbank) (>> Korporativna targovska banka AD Sofia), the country's fourth largest.

"There are attempts aiming to destabilise the banking system and there's an investigation in this direction since yesterday," Yovchev said.

"There was an attack through the Internet and through mobile phones, they have sent SMS and to disturb people randomly, as the aim was to spread the rumour to destabilise a certain bank," he said. "The state has the resources and the tools to respond to any malicious attack."

(Reporting by Angel Krasimirov; writing by Matthias Williams; Editing by Gareth Jones)