The UK has "glaring gaps" in its ability to defend the Arctic region, leaving it vulnerable to potential Russian attacks, a report by MPs has warned.
The Commons Defence Committee said a shortage of Royal Navy warships and submarines was leaving the country's critical infrastructure in the High North, including undersea cables and energy supplies, exposed.
In the event of a conflict, the report added that Russia could threaten the UK's population, civilian and military infrastructure and vital supply routes across the Atlantic from the US.
The Ministry of Defence (MoD) said it is "clear-eyed about the threat Russia posed" and is investing heavily to protect Britain's undersea cables.
Former Prime Minister Sir Keir Starmer previously warned that Russia could attack Nato by the end of the decade.
The High North - which includes the Arctic circle and areas adjacent to it - has become central to the UK's defence concerns in recent years.
Earlier this year, the MoD said Russian submarine activity in the North Atlantic is now back to the same levels as the Cold War era.
In the new report, MPs highlighted a "shockingly low availability" of submarines and said there was a temporary loss in ability to operate them beneath Arctic ice.
"Russia can then use the ice to conceal and protect its own submarines while threatening Nato sea lanes, UK critical infrastructure and the UK's nuclear deterrent," it added.
Chair of the Defence Committee, Tan Dhesi, said: "This is a demanding, hostile environment, and one that our greatest adversary, Russia, is seeking to dominate for military advantage."
The work to address these gaps "cannot start soon enough," he added.
In light of uncertainty over US support for Nato, the report said the UK should consider whether the British-led Joint Expeditionary Force (Jef), a UK-led military coalition of northern European nations, should focus more on the High North.
An MoD spokesperson said the Jef was already "strengthening Nato's northern flank and increasing our ability to respond rapidly to emerging threats".
Conservative shadow minister for war readiness Stuart Anderson said: "If Nato could be at war with Russia as soon as 2030, as the former prime minister warned, that means time is just as important as money.
"To deter war we must be ready for it, that means spending money now, not kicking the can down the road until it's too late".