The warning comes after Russia conducted large scale military exercises last year, including simulated attacks across northern Europe, from Kaliningrad to Lithuania, the BBC reports.

In the speech, which will take place at the Royal United Services Institute on Monday, Gen Sir Nick Carter will highlight Russia's new cyber warfare capabilities.

Gen Carter will also highlight the Russian army's long-range missile strike capability. While Russian forces were intervening in Syria, 26 missiles were deployed from a 1,500km (930 mile) range.

He will add that Russia is building an increasingly aggressive expeditionary force, which already boasts capabilities the British Army would struggle to match.

Read alsoRAF jets scrambled to intercept Russian bombers less than 35 miles from UK airspace - mediaPotential military threats to the UK "are now on Europe's doorstep," Gen Carter will say.

Last year Prime Minister Theresa May said Russia had "mounted a sustained campaign of cyber espionage

This intervention from Gen Carter is as much an appeal for more money to fund the armed forces and to avoid further cuts.

There are concerns in the armed forces that the review will prioritize counter-cyber attacks and terrorism, rather than major defense.

Read alsoLatvian man who fought for Ukraine in Donbas allegedly burned to death in car in British Crown territoryLast week Conservative MP Julian Lewis, chairman of the Commons defense select committee, posed an urgent question in the Commons after speculation that there were plans to cut the UK military by 14,000 service personnel, nine warships and 100 helicopters.

Mr Williamson said "hard work" is taking place to give the armed forces the "right resources".

Some MPs have called to increase defense spending to 3% of GDP, the BBC wrote.