KABUL — US military authorities are investigating a video widely circulated on Afghan social media that apparently shows a US service member firing into a civilian truck driving along a road in Afghanistan, a spokesman said.

"The video in question is not official, not authorized and does not represent the professionalism of the service members of US Central Command," Air Force Col. 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," he said.

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 Thomas said had caused "serious concern", comes as the United States has stepped up operations in Afghanistan against both Taliban insurgents and radical fighters from the Daesh (so-called IS) group 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 casualties 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," Gen. 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