US Marines who posed for a photograph with a flag combining the Nazi SS insignia with the Stars and Stripes will escape punishment after military bosses said it was a naïve mistake.

The US sniper team were put under investigation after the photograph, taken in Afghanistan in September 2010, surfaced on the net.

The photo, published on a blog by a military weapons company called Knight's Armament, shows 10 marines posing with the "lightning bolt" icon worn by fascist SS forces during the Second World War.

The marines are believed to be by members of 1st Reconnaissance Battalion based in the Sangin district of Helmand province.

Marine Corps authorities said after investigations that the soldiers had no intention of associating themselves with the SS - who were responsible for murdering millions of Jews, gypsies, gays and communists during the war and instead believed the "SS" stood for "Scout Snipers".

"The incident was found not to be racially motivated. Those involved acknowledged that the symbol could be misinterpreted and is not in keeping with our Marine Corps ethos and values," military spokesman, Mark Oliva, told AFP.

"They didn't realise that they were associating themselves with something that was racist or fascist.

"They saw 'SS' and associated it with 'scout sniper' rather than the Nazis," Oliva said.

The Marine Corps added: "The commander determined that disciplinary action was not warranted. Further, all Marines in the unit were reminded that any such behaviour would not be tolerated and further display could result in punishment."

The photograph is the latest scandal to hit the Marine Corps and follows the release of a video showing men in US Marine uniforms apparently urinating on the corpses of Taliban soldiers.