According to the Theocratic Government of Iran, with whom the US just "delayed" their production of nuclear weapons by ten years; the Holocaust did not happen.

That is one reason that they are authorized and intend to "destroy the state of Israel". 

"In his official 2013 Nowruz address, Supreme Leader of Iran Grand Ayatollah Ali Khamenei questioned the veracity of the Holocaust, remarking that "The Holocaust is an event whose reality is uncertain and if it has happened, it’s uncertain how it has happened.”

" Ahmadinejad said that a legend was fabricated and had been promoted to protect Israel. He said:
"They have fabricated a legend, under the name of the Massacre of the Jews, and they hold it higher than God himself, religion itself and the prophets themselves."