The Chief of the Defence Staff has warned of Russia's threat at sea, and of how their submarine activity is threatening worldwide communications systems.
Admiral Sir Tony Radakin said underwater cables that transmit internet data are "the world's real information system", adding any attempt to damage them could be "an act of war".
Speaking to the Times in his first interview as head of the UK's Armed Forces, Admiral Radakin, the former Royal Navy chief, said there has been a "phenomenal increase in Russian submarine and underwater activity over the last 20 years".
"Russia has grown the capability to put at threat those undersea cables and potentially exploit those undersea cables," he said.
He said that meant Moscow could "put at risk and potentially exploit the world's real information system, which is undersea cables that go all around the world".
The Royal Navy has been tracking Russian submarine activity, with a collision between HMS Northumberland and a Russian submarine sparking speculation about cable-mapping activity.
Watch: Dramatic moment HMS Northumberland collides with Russian sub in 'eyewateringly expensive' incident.
The collision occurred in December 2020, after the ship engaged in a high stakes game of cat and mouse with the underwater vessel.
Admiral Radakin also said the UK needed to develop hypersonic missiles in order to keep up with military competition - highlighting Russia's hypersonic and long-range missile capability as a threat and the UK's comparative ability as a weakness.
He also said he had briefed ministers on Britain's "military choices" if Russia launched an invasion of Ukraine, but did not reveal any further information.
Defence Secretary Ben Wallace has previously said it would be "highly unlikely" the UK would send troops if an invasion occurred.
Talks between Moscow, the US and NATO are scheduled for next week amid tensions sparked by a Russian military build-up on the Ukraine border.
However, NATO general secretary Jens Stoltenberg has said the alliance needs to prepare "for the possibility that diplomacy will fail".
Foreign Secretary Liz Truss called on Friday for Russia to end its "malign activity" towards Ukraine.