German authorities are investigating members of a British far-right group for posting a photo on social media showing themselves doing a "Hitler salute" at the former Buchenwald concentration camp.

According to German daily Bild published a photograph Thursday it says was posted on a National Action website showing a blurry image of two people holding the far-right group's flag inside the basement of Buchenwald's crematorium.

A spokeswoman for the Buchenwald Memorial site says the room was once used to store corpses, but the Nazis also strangled over 1,000 people on metal hooks there.

Sandra Siegmund says officials filed a criminal complaint to police Wednesday after being informed of the picture.

About 250,000 prisoners were held at Buchenwald between July 1937 and April 11, 1945. An estimated 56,000 people were killed.