KYIV (REUTERS) - The online networks of Ukraine's defence ministry and two banks were overwhelmed on Tuesday (Feb 15) and Ukraine's information security centre pointed the finger at neighbouring Russia.

"It is not ruled out that the aggressor used tactics of little dirty tricks because its aggressive plans are not working out on a large scale," the Ukrainian Centre for Strategic Communications and Information Security, which is part of the culture ministry, said in a statement.

Kyiv has blamed Moscow for similar actions in the past and since Russia began massing more than 100,000 troops near the frontier, raising East-West tensions as the West fears Russia is planning to attack Ukraine, which Moscow denies.

The type of disruption reported by Ukrainian authorities on Tuesday is known as a distributed denial-of-service - often abbreviated DDoS - but the scale of it wasn't immediately clear.

The manoeuvre, which works by directing a fire hose of internet traffic from a multitude of sources against one set of servers or another, is a common across the internet and such attacks happen periodically in Ukraine and beyond.

A message on the home page of the Ukrainian defence ministry website said it was under maintenance. The ministry tweeted that its website was apparently under a cyberattack and it was working on restoring the access to it.

Oshadbank confirmed the cyberattack saying that it resulted in slowing down of some of its systems. The strategic communications centre said that Privatbank users also had problems with payments and a banking app. Privatbank did not immediately comment.

San Francisco-based Cloudflare, a prominent provider of denial-of-service protection, said that it had seen no evidence of "large DDoS activity" in Ukraine against its data centres or customers there.

"From our perspective today hasn't seen unusual attack traffic against us or our customers on Ukraine," the company said in an email.

The United States and its allies have indicated that they are prepared to respond to Russian digital incursions, even if details remain sparse.

White House press secretary Jen Psaki said there were "a range of means that we could respond - both seen and unseen - to a cyber attack or any other attack."