Russia “indisputably” poses a far greater threat to national security than Islamic terrorist groups such as al-Qaida and Isis, the new head of the British army has warned.

General Mark Carleton-Smith said the UK cannot be complacent about the threat Russia poses “or leave it uncontested”.

The former SAS commander said Russia had made plain its preparedness to use force to expand its interests, while it had also been “systematic” in its efforts to exploit cyber space and undersea military arenas.

“The Russians seek to exploit vulnerability and weakness wherever they detect it,” he told the Daily Telegraph.

“Russia today indisputably represents a far greater threat to our national security than Islamic extremist threats such as al-Qaida and Isil,” he said, using another name for Isis.

Carleton-Smith, who graduated from Sandhurst in the final years of the Cold War, took over as chief of the general staff in June.

He led the hunt for Osama bin Laden after the 9/11 terror attacks and later spearheaded Britain’s role in the campaign to defeat Isis.

Now, with the threat from Islamist groups in the Middle East reduced by years of concerted international military action, the focus needs to shift to Russia, he said.

“We cannot be complacent about the threat Russia poses or leave it uncontested,” Carleton-Smith warned.

Russia has been the subject of international condemnation over its annexation of Crimea and continued involvement in conflict in Ukraine that also saw it blamed for the downing of Malaysia Airlines flight MH17.

The Kremlin has also been accused of aggression in cyber space, including meddling in the 2016 US election and attacks on a number of Western interests.

Its military intelligence unit, the GRU, is suspected of having a global reach and has been accused of being responsible for the nerve agent attack in Salisbury.

In October defence secretary Gavin Williamson accused Russia of acting like a “pariah state”.

Countering Russia’s suspected efforts to destabilise the established world order has led to debate over the role of Nato – including president Donald Trump’s threats over the US’s contribution – and suggestions of other means of international cooperation.

Earlier in November French president Emmanuel Macron called for the creation of a “true European army” to make up for any loss of support from Washington.

Carleton-Smith said he would not support any initiative that “diluted” the military effectiveness of Nato. He said the alliance represents the “centre of gravity of European security” and insisted it has been “extraordinarily successful”.

“In my experience, we should reinforce success,” he said.