Britain's ability to pre-empt or respond to threats risks being eroded if the UK does not keep up with its enemies, the head of the British Army is to warn.
General Sir Nick Carter is also expected to highlight how Russia, in building an increasingly aggressive and expeditionary force, already boasts capabilities the UK would struggle to match.
During a speech at the the Royal United Services Institute today (January 22) he will point to Syria, where he will say the Kremlin has repeatedly and publicly demonstrated its long-range strike capability.
Carter will add that Britain must also look closely at how countries are now being more creative in the ways in which they exploit the seams between peace and war.
"Our ability to pre-empt or respond to threats will be eroded if we don't keep up with our adversaries," the chief of the general staff is expected to say today (January 22).
"State-based competition is now being employed in more novel and increasingly integrated ways and we must be ready to deal with them.
"The threats we face are not thousands of miles away but are now on Europe's doorstep - we have seen how cyber warfare can be both waged on the battlefield and to disrupt normal people's lives. We in the UK are not immune from that."
Mirroring Kremlin concerns made by others, General Carter will also highlight how last year Russia undertook simulated attacks across Northern Europe - from Kaliningrad to Lithuania.
Last month the chief of the defence staff, Air Chief Marshal Sir Stuart Peach, also addressed the threat of Russia, and said the UK's military has prioritised the protection of undersea cables from the Kremlin, because if they are cut or disrupted there would be an immediate and "potentially catastrophic" hit to the economy.
Using her address at the Lord Mayor's Banquet in London, Theresa May also said last year that Russia had "mounted a sustained campaign of cyber espionage and disruption" against other countries.
Carter's comments come during a period of widespread speculation about possible cuts to personnel and equipment amid major pressure on the defence budget.
There have been calls to increase defence spending to 3% of GDP from some MPs, and reports there are plans to cut the armed forces' strength by more than 14,000, as well as the combination of elite units of paratroopers and Royal Marines to save cash.