New York, Jan 25 (IANS): Amid the heightened Russia-Ukraine border tensions, the US' Department of Homeland Security (DHS) has warned that critical infrastructure and local government networks are at a "very high risk" of a mega cyber attack sponsored by the Russian government.

First reported by CNN, the DHS notice said that Russia "maintains a range of offensive cyber tools that it could employ against US networks -- from low-level denials-of-service to destructive attacks targeting critical infrastructure".

"We assess that Russia would consider initiating a cyber attack against the Homeland if it perceived a US or NATO response to a possible Russian invasion of Ukraine threatened its long-term national security," the notice further read.

DHS has sent the memo to state governments, local governments, and operators of critical infrastructure.

Despite the US tensions with Russia over Ukraine, the DHS assesses that Moscow's threshold for conducting disruptive or destructive cyberattacks on the US homeland "probably remains very high".

The US Department of Defense has announced that nearly 8,500 US troops have been put on heightened alert for a possible deployment due to escalating tensions on the Russia-Ukraine border, but there is no decision on formal deployments.

US President Joe Biden last week stressed that the country would respond with its own cyber attacks if Russia continues to target Ukrainian government websites.

Russia-sponsored hackers earlier hit Ukraine with a massive cyber-attack, shutting down several government websites. As a result of the cyber-attack, the websites of the Ministry of Foreign Affairs and a number of other government agencies went down.

Russia has repeatedly been accused of cyber-attacks against Ukraine amid escalated tension between them.

The European Union (EU) is also prepared to defend against any possible Russian cyber-attacks or hybrid threats if it invades Ukraine and is "very well advanced" in its preparation for a response to any aggression.