The Pentagon said Thursday it had opened an investigation after a video posted online appears to show an American soldier firing a shotgun at the driver of a civilian truck in Afghanistan.

The incident is nestled within a three-minute video, overdubbed with hip-hop music, that is a compilation of macho, helmet-cam footage showing US special operations forces at work in Afghanistan.

One brief clip amid the footage shows an armored vehicle driving past a truck.

The arms of a person wearing gloves and camouflage can be seen pointing a shotgun at the cab. The driver's side window then shatters.

However, the short clip does not show what happened to the driver.

"The amateur video posted on a public website gives us serious concern," the US military's Central Command said in a statement.

"The video in question is not official, not authorized and does not represent the professionalism of the service members of US Central Command. We are conducting an investigation into this video, and will take appropriate actions as a result of this investigation."

According to Politico, the video was posted on YouTube and was called "Happy Few Ordnance Symphony."

It was quickly taken down but can still be found online at other sites.

Centcom chief General Joe Votel said he had seen the video.

"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," Votel said in a statement.

"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."

Other sequences in the video show first-person footage of machine gunners raking buildings and hillsides with gunfire, and commandos launching mortars and small rockets.

One gunner has a "Trump" sticker attached to his gun turret, indicating the video was shot in the past year.