Russia's telecom operator on Friday said it had blocked a series of cyberattacks on the country's leading banks this week, the latest to target Moscow's financial sector.
Rostelecom said in a statement it "successfully thwarted DDoS [distributed denial of service] on the five biggest banks and financial organisations in Russia" on Monday.
"The most sustained attack lasted more than two hours," it said.
Russia's FSB security service last week said it had uncovered plans by foreign intelligence services to carry out massive cyberattacks on the country's financial system from December 5.
State-controlled Russian bank VTB said on Monday that its websites had been hit by a cyberattack but insisted its systems were still working "as normal".
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 United States over allegations by 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 comes after Moscow-based security giant Kaspersky said in November a massive DDoS cyber-attack 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 US.