A Russian submarine which could attack gas pipelines was tracked near the Shetland Islands where an underwater cable was damaged, a former defence chief has said.
Two breaks in lines connecting Shetland to the Scottish mainland and the Faroe Islands caused a widespread communication breakdown on 20 October.
The situation led police to declare a major incident, with phone and internet services cut.
Former security minister Lord Alan West said it was important to keep an eye on foreign ships when they entered British waters but added he did not suspect it was Russia that damaged the cable.
On Tuesday, Lord West, the former head of the Royal Navy, told Talk Radio: “In the Shetlands recently, where power was lost a couple of times and I’m sure it was probably a dredger or a trawler did it.
“But actually there was a Russian ship of the type that can cause damage to damaged pipelines in that region.
“And hopefully, we are monitoring very closely making sure we’re seeing what they are doing.”
The Auxiliary Shipping Forecast blog reported that Russian research ship Akademik Boris Petrov sailed through the Shetland-Orkney Gap a day after the cable was damaged on 21 October.
The damaged underwater cable has since been repaired.
Lord West also accused Vladimir Putin and his government of spreading lies about all sorts of issues, including alleging that British Navy personnel blew up the Nord Stream gas pipelines in September.
The UK said the claim was false and designed to distract from Russian military failures in Ukraine.
Lord West called the allegation “laughable” but added there was a worrying aspect because it could be used to justify retaliation, like cutting a gas pipeline for Norway to the UK.
He added: "The Russians for many years have had a thing called Maskirovka. That is spreading alarm and confusion. It's their way of fighting wars."
General Sir Richard Barrons also warned Russia could use unfounded claims that Britain was involved in attacks on critical Russian infrastructure as a pretext for disrupting energy supplies from Norway to the UK.
The Russian ministry alleged that "British specialists" from the same Navy unit directed Ukrainian drones packed with explosives in attacks on ships in its Black Sea fleet in Crimea at the weekend.
General Sir Richard told Times Radio that while it is "clearly ridiculous" to claim that British experts were involved in the drone stroke, it is an "indication of how Russia's eye is turning to the supporters of Ukraine".
He said: "We shouldn't be surprised if we too get a tough time, whether it's in cyberspace or electricity generation, or whatever it is, in the coming weeks and months."
On Thursday, the US released plans to better track weapons supplied to Kyiv, over fears Russian forces could capture them and use them to fabricate attacks by Ukrainian forces.
It followed unfounded claims that Ukraine was planning to use a "dirty bomb" on Russian soil, which officials in the Washington, London and Paris feared as an excuse to escalate the war.