The British Army said on Wednesday it is investigating after a video emerged showing soldiers on a shooting range firing at a picture of opposition Labour leader Jeremy Corbyn.

The 26 seconds of footage shared on social media, reportedly recorded in Afghanistan's capital Kabul, shows four army personnel shooting at an image of the veteran left-wing leader.

"We are aware of a video circulating on social media," an army spokesperson said.

"This behaviour is totally unacceptable and falls well below the high standards the Army expects.

"A full investigation has been launched."

A Labour Party spokesperson said: "This behaviour is alarming and unacceptable. We have confidence in the Ministry of Defence to investigate and act on this incident".

Britain's Press Association said it understood the soldiers had fired a non-lethal hardened wax substance instead of metal bullets at the Corbyn image, which is pockmarked in the footage.

It said the incident is believed to have taken place in the past few days and involved soldiers from the army's 3rd Battalion Parachute Regiment.

The range is on a compound in Kabul where personnel practice "guardian angel" drills protecting VIPs, according to Sky News.

Images of celebrities feature at the site, but for use as targets to be protected rather than shot at, it added.

"If authentic this is unacceptable," junior defense minister Tobias Ellwood said on Twitter, vowing that he was "looking into it".

Corbyn, 69, a leftist stalwart, is a reviled figure among many British Conservatives and right-wingers who label him a Marxist.

A low-level fixture of British politics for four decades, he unexpectedly took control of the Labour Party in 2015 on a proudly socialist programme.

A proclaimed pacifist, Corbyn has promised to make "conflict resolution and human rights" central to Britain's foreign policy if he took power, and to be "guided by the values of peace, universal rights and international law."