They may be right-wing, but denigrating a Holocaust memorial is going too far, even for Germany's up-and-coming Alternative for Germany (AfD) party.

On Monday its leaders overwhelmingly voted to launch an internal investigation that could lead to the expulsion of Bjoern Hoecke, leader of its branch in the former East German state of Thuringia.

At issue is a speech he made last month to young party supporters in Dresden, in which he called Berlin's Holocaust memorial a "monument of shame".

Ten days later, he was barred from taking part in a Holocaust Remembrance Day ceremony at the Buchenwald Concentration Camp Memorial.

Supporters of the procedure said Hoecke had endangered the party with his remarks, which could cause an exodus of voters. But critics said his potential expulsion could also bring about a loss of party members who sympathise with him.

Hoecke is far from the first person to be called out for far-right views by fellow AfD members.  Last July, the party chastised one of its newly elected politicians, Wolfgang Gedeon, for antisemitic writings.

Gedeon is still on the Baden-Württemberg state parliament, but not as a member of the AfD's bloc.

More recently, the party's fraction in Bavaria has launched an internal investigation into Elena Roon - who is running for a seat in the Bundestag  - after she published a photograph of Adolf Hitler in an online chatroom, with the caption, "Missing since 1945: Adolf, please come back! Germany needs you!" Reportedly, under another image of a distraught Hitler she wrote, "Islamists... I forgot about them!"