Iran's supreme leader Ayatollah Ali Khamenei on Friday voiced doubts about the existence and scale of the Holocaust, questioning the West's "red lines" on freedom of expression.
In Europe, "no one dares to speak of the Holocaust, the crux of which is not clear if it is true, or if it were, how it was," Khamenei said in remarks broadcast live from the northeastern city of Mashhad.
Khamenei, Iran's top decision-maker, has repeatedly called Nazi Germany's killing of six million Jews a "myth" and said the historical record has been distorted.
Iran does not recognise Israel, and its leaders have regularly called for it to be wiped off the map as mutual hostility has escalated over Tehran's controversial nuclear programme.
President Hassan Rouhani, a self-declared moderate, has adopted a softer line, going so far as to condemn "the massacre of the Jews by the Nazis."
In February, Foreign Minister Mohammad Javad Zarif irked hardliners in Tehran by describing the Holocaust as a "cruel tragedy which should never happen again."
On Friday, Khamenei appeared to draw parallels between "red lines" in the West over discussion of the Holocaust and Iran's own policies regarding freedom of expression.
In his speech marking the Persian New Year, Khamenei called for "resistance" in the face of a "cultural invasion" targeting the Islamic state's religious beliefs.
"Expressing opinion about the Holocaust, or casting doubt on it, is one of the greatest sins in the West. They prevent this, arrest the doubters, try them while claiming to be a free country," he said.
"They passionately defend their red lines ? how do they expect us to overlook our red lines that are based on our revolutionary and religious beliefs," he asked without elaborating.
Iran's human rights record and its limits on free expression are routinely criticised by international organisations and Western powers.
Last week, UN chief Ban Ki-moon strongly criticised Iran for an increase in executions, the detention of dissidents and discrimination against women.