German authorities are investigating a British far-right group over a photo on social media showing members performing a “Hitler salute” at the former Buchenwald concentration camp.

Media outlet Bild published a photograph on Thursday that 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 more than 1,000 people on metal hooks there.

Sandra Siegmund says officials filed a criminal complaint to police on 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.

Karen Pollock, Chief Executive, Holocaust Educational Trust said: “To enter a concentration camp and perform the Nazi salute is nothing more than a salute to their own idiocy – their openly anti-Semitic attention seeking is a deliberate attempt to belittle the memory of the Holocaust, insult survivors and cause offence to the Jewish people.”

National Action's tweet of two members doing the salute in Buchenwald

National Action’s tweet of two members doing the salute in Buchenwald