British special forces are hoping to be given a new remit to counter Russia and other state actors as secret missions against Islamic State targets in Syria and Iraq become less necessary.

The idea, first reported by BBC’s Newsnight, has been worked up for ministers and would involve a new focus for the SAS and other parts of the special forces, the most secretive parts of the British military.

The director of special forces has drawn up a plan in confidence named “Special Operations Concept”, which will soon be considered by ministers. If approved the scheme would involve a restructuring of the relevant units.

Underlying the plan is a belief that the nature of modern warfare is changing, with less emphasis on conventional military action and instead a shift towards a more subtle conflict between nation states.

Two tankers were targeted in the Gulf of Oman on Thursday morning, a sophisticated covert attack that the US blamed on Iran. Tehran denied responsibility and its foreign minister suggested others could be trying to provoke a conflict.

Last week, Gen Sir Mark Carleton-Smith, the chief of general staff, talked about the emerging thinking in British circles, saying that peace and war were “two increasingly redundant states”.

In a clear reference to Russia, Carleton-Smith said authoritarian regimes were “exploiting the hybrid space that exists in between” – disinformation, subversion or cyber – where lives may not immediately be at stake but economies, livelihoods and ways of thinking are.

Concern about Russia has soared in the aftermath of the poisoning of the Skripals in Salisbury last year. That was blamed on Russian military intelligence, the GRU, whose activities a restructured special forces hopes to counter.

Over the last decade and a half, British special forces have been active on covert missions in Syria, Iraq and Afghanistan. But with Isis losing the last of its territory in March, the military believe it is time to move on.

One Whitehall source told the BBC: “The counter-terrorist task is drawing down, while the need to confront dangerous international behaviour by peer adversaries [nation states] is increasing.”

Britain’s special forces comprise the the regular Special Air Service regiment, which is the best known of the units plus the Special Boat Service, and Special Reconnaissance Regiment, tasked with covert surveillance.

The last of these three would become more important and would work more closely with MI6 and also other western intelligence agencies.

The Ministry of Defence did not comment. It has a policy of not discussing the activities of the special forces.