A decision by soldiers to shoot at an image of Labour leader Jeremy Corbyn was a “serious error of judgment”, a senior military commander has said.

Footage captured in Kabul, Afghanistan, shows personnel from 3rd Battalion, Parachute Regiment using a picture of the Islington North MP for target practice on a Simunition range.

Brigadier Nick Perry, commander of 16 Air Assault Brigade, said the Army is conducting a full investigation and wants to get to the bottom of what happened.

“This is a serious error of judgment,” Brig Perry said. “Let me be clear – the Army is, and always will be, an apolitical organisation.

“We have 400 soldiers from the Brigade conducting force protection in Afghanistan, and working closely with both Nato and Afghan partners. These soldiers are doing an outstanding job out there.”

A Labour Party spokesman described the conduct of the soldiers in the clip as “alarming and unacceptable”, adding that they have confidence in the Ministry of Defence to investigate and act on the incident.

Defence Secretary Gavin Williamson said he commends the “prompt and clear leadership shown by the Army in investigating this troubling video”.

An Army spokesman said they are aware of the clip circulating on social media.

“This behaviour is totally unacceptable and falls well below the high standards the army expects, a full investigation has been launched,” he added.

The video shows a number of soldiers taking aim down the range and firing their weapons – the camera then focuses on the target and zooms in on an image of Mr Corbyn.

With a graphic of “happy with that” across the screen throughout, a number of marks can be seen peppered across Mr Corbyn’s face.

It is understood it was a non-lethal hardened wax substance aimed and fired at the image instead of metal bullets, with the incident taking place in the past few days.

The range is designed for and used by personnel to practise what is called the “guardian angel drill” – a force protection tactic.

Theresa May’s official spokesman said the incident was “clearly unacceptable”, and that the Prime Minister was aware of the video’s content but had not seen it.

Commons speaker John Bercow also condemned the footage and said he would be “horrified” if service personnel behaved in such a way towards an MP.

Shadow defence secretary Nia Griffith has written to her Tory counterpart, Mr Williamson, asking him to “condemn this footage immediately” and “commit to ensuring that the investigation is thorough and carried out in a timely manner”.

In the letter posted on Twitter, she added that the “appalling footage comes at a time when members of Parliament face an unprecedented level of threat to their personal safety”.

Former soldier and Tory MP Johnny Mercer tweeted that “every organisation has good people who make serious misjudgements”.

He added: “It’s how it police’s itself that matters, and an inability to do that correctly has caused so many problems of late (IHAT). I look forward to a robust response.”

Labour MP Dan Jarvis, who is also a former Paratrooper, said the incident is “shameful and utterly unacceptable”.

“This goes against the values and standards of the British Army. I welcome the Ministry of Defence investigation into this video and trust it will be resolved quickly,” he added.

The incident was also branded as “deeply worrying” by Labour MP Paul Sweeney who served as an Army reserve soldier for 12 years.

He said what the soldiers in the video have done is a “shameful act which destroys the reputation of the British Army”, and is at odds which what is expected of them.

“They need to be held to account for that action, but it demonstrates a more worrying trend in our society, where we’re prepared to see that kind of behaviour enacted against a key part of our democracy,” he told the Press Association.

“Whether you like him or not, Jeremy Corbyn is the Leader of Her Majesty’s Official Opposition in Parliament, and Parliament is the supreme democratic body in this country.”

It comes after far-right activist Tommy Robinson posted a photograph of himself surrounded by grinning soldiers in October – prompting another Army probe.

The former English Defence League leader also shared a video featuring Army personnel who cheered and shouted his name.

At the time, the Army said it was aware of the image and footage and was “investigating the circumstances”, adding that a “far-right ideology is completely at odds with the values and ethos of the armed forces”.