A US military colonel says there is "serious concern" over a video appearing to show an American soldier firing into the front window of a civilian truck in Afghanistan.

Key points: The video shows what appears to be a US service member firing into a civilian truck in Afghanistan

The video shows what appears to be a US service member firing into a civilian truck in Afghanistan The footage has been circulated on social media

The footage has been circulated on social media US authorities say the video has caused serious concern

Authorities will investigate the footage, which has been widely circulated on Afghan social media, a spokesman said.

"The video in question is not official, not authorised and does not represent the professionalism of the service members of US Central Command," Air Force Colonel John Thomas, a spokesman for the US military Central Command, said in an emailed statement.

"We are conducting an investigation into this video, and will take appropriate actions as a result of this investigation."

It was not clear when or where the video was made.

The clip, filmed from the perspective of the apparent shooter as they sit in a moving vehicle, shows a civilian truck being overtaken when a shot appears to be fired into its window.

The video, which Colonel Thomas said had caused "serious concern", comes as the US has stepped up operations in Afghanistan against both Taliban insurgents and radical fighters from Islamic State and other militant groups.

Commanders have been very sensitive to reports of civilian casualties, mindful of the serious tensions with the Afghan government and public opinion caused by such incidents in previous years.

"I have reviewed the video and I am disappointed and also concerned that the American people, our Coalition partners, the Afghan government, and the Afghan people will believe that American service members are callous and indifferent to the horrors of war or the suffering of innocent people trapped in conflict," General Joseph Votel, Commander, US Central Command, said in the emailed statement.

"I can assure you that this video does not represent the professionalism or humanity of the men and women of US Central Command. We reject the unprofessional and callous message this video conveys," he said.

Reuters