Hamid Reza Asefi, a Foreign Ministry spokesman, said on Tuesday: "The comments by Prime Minister Tony Blair are an insult to the intelligence of people around the world.
"For half a century, the defenders of the Holocaust have used every tribune to defend their position, and now have to listen to others."
The Foreign Ministry announced plans for the conference last week, a month after Mahmoud Ahmadinejad, the Iranian president, described the systematic slaughter of an estimated six million Jews during the second world war as a "myth".
On Monday, Blair branded the plan "shocking, ridiculous, stupid" and said Ahmadinejad "should come and see the evidence of the Holocaust himself in the countries of Europe".
But Asefi said Iran had a right to "hear all opinions" on the Holocaust "and chose the best one".
"Why are the defenders of globalisation insisting, like in the Middle Ages, on their unilateral position and for the global village to speak as one voice?"
Hamid Reza Asefi,
Iranian Foreign Ministry spokesman
"Why are the defenders of globalisation insisting, like in the Middle Ages, on their unilateral position and for the global village to speak as one voice?
"Sadly, blind intolerance and political interests and objectives have closed the eyes of the Holocaust defenders to the realities of the world, and they even reject the very principle of a scientific conference."
Ahmadinejad, an ultra-conservative who came to power in a surprise victory last June, has provoked international condemnation with a number of anti-Israeli remarks.
They include labelling Israel a "tumour" that should be "wiped off the map" or moved as far away as Alaska, and claiming the Holocaust was a Western invention.
The Foreign Ministry has yet to fix a date for the event.