State-controlled Russian bank VTB said Monday that its websites had been hit by a cyberattack but insisted its systems were still working "as normal".
"A DDoS (distributed denial of service) attack was carried out against VTB Group internet sites," Russia's second largest bank said in a statement carried by Russian news agencies.
"Our IT infrastructure is working as normal and the bank's clients are not experiencing any difficulties."
Russia on Friday said it had uncovered plans by foreign intelligence services to carry out massive cyberattacks this month targeting the country's financial system.
The FSB security service said in a statement that it had received information on "plans by foreign secret services to carry out large-scale cyberattacks from December 5".
The FSB did not say which countries' secret services were involved in the latest plot against Russian banks but alleged the attacks would use servers and "command centres" located in the Netherlands belonging to Ukrainian hosting company BlazingFast.
Russia has been embroiled in a hacking scandal with the US over allegations from Washington that Moscow was behind the theft and leaking of documents online during the run-up to the US presidential election aimed at influencing the outcome.
Vice President Joe Biden warned that the US would respond to the suspected Russian hacking "at the time of our choosing and under the circumstances that have the greatest impact".
The latest attack on VTB comes after Moscow-based security giant Kaspersky said in November that a massive DDoS cyberattack had hit at least five of Russia's largest banks.
DDoS attacks involve flooding websites with more traffic than they can handle, making them difficult to access or taking them offline entirely.
Kaspersky said those attacks used devices located in 30 countries including the United States.
Russia's largest lender, state-controlled Sberbank, acknowledged it had been hacked but said its operations had not been interrupted.