Iran's former reformist president Mohammad Khatami has described the Holocaust as a "historical reality" - a stinging attack on his controversial and revisionist successor Mahmoud Ahmadinejad. "We should speak out if even a single Jew is killed. Don't forget that one of the crimes of Hitler, Nazism and German national socialism was the massacre of innocent people, among them many Jews," the cleric said in comments carried in the Iranian press on Wednesday.The Holocaust, he asserted, should be recognised "even if this historical reality has been misused and there is enormous pressure on the Palestinian people".