Iranian Supreme Leader Ayatollah Ali Khamenei questioned the Holocaust on Friday morning in an address marking Nowruz, the Persian New Year.
The "Holocaust is an event whose reality is uncertain and if it has happened, it's uncertain how it has happened," Khamenei was quoted as saying on his Twitter account.
In the latest instance of an Iranian leader's refusal to recognize the Holocaust, Khamenei claimed that Europe remained silent over its occurrence.
The remarks by Iran's most powerful leader came a day after President Shimon Peres reached out to the Iranian people in a holiday greeting, appealing for Israel and the Islamic Republic to "forget war and threatening" and have a year of "silence and peace".
In his speech made to large crowds in Iran's northeastern city of Mashhad, Khamenei turned to the Israeli-Palestinian peace process and chided the US in its role in what he said were failed negotiations.
He also accused the US alongside Israel of conspiring to rid the region of Palestinians - both Muslim and Christian.
“The US has failed in Palestine. They devised a scheme against Palestine and spared no efforts [in carrying it out],” Iran's official Press TV quoted Khamenei as saying.
Khamenei's rhetoric came as "moderate" President Hassan Rouhani has pledged to improve Iran's image in the international arena after his predecessor Mahmoud Ahmadinejad had tarnished it often, made inflammatory remarks about Israel and denying the Holocaust.
The President of the World Jewish Congress Ronald Lauder expressed dismay over Khamenei's comments on Friday.
“When countries are rushing to welcome back a supposedly more moderate Iran into the world community and to do business with it, they should remember, it is not a new Iran, but the same Iran with a new face,” Lauder said.
“Ayatollah Khamenei's words are unmistakable: he denies the Holocaust happened. Iran needs to renounce Holocaust denial, extremism, and bigotry if the world is to have any faith in its conduct and intentions. Until then, the West needs to be very careful in in engaging with Tehran,” he added.
In September, Rouhani was quoted by CNN as condemning the Holocaust. Iranian media later accused CNN of fabricating Rouhani's comments.
Foreign Minister Mohammad Javad Zarif apparently receive backlash in February over public comments condemning the Holocaust when Islamic hardliners in Iran's parliament reportedly summoned him after making the remarks.
Zarif caused an uproar among conservatives in the Islamic Republic when he called the Holocaust a "horrifying tragedy" in an interview with a German television station late last month.