As sirens wailed across Israel at the stroke of 10:00am (0700 GMT), the country stopped for two minutes in remembrance of the six million victims of the genocide in World War II.

Cars pulled over on motorways and pedestrians were rooted to the spot as citizens paid solemn tribute to their ancestors who perished in concentration camps and gas chambers.

Around 5,0000 Israelis were also taking part in the annual three-kilometre (two-mile) march in Poland from the red-brick barracks of Auschwitz to the gas chambers in Birkenau where at least 1.1 million people died.

But the commemorations, which began on Monday evening at Jerusalem's Yad Vashem Holocaust memorial, were also marked by warnings about the intentions of Ahmadinejad who has called for the Jewish state to be "wiped off the map."

Shimon Peres, Israel's former prime minister, drew a direct comparison between Ahmadinejad and the leader of Nazi Germany in an interview from Poland where he was to lead the March of the Living.

"This is the first man since Hitler to stand up and say that the Jewish people must be exterminated," the Nobel peace prize winner told public radio.

"Hitler prepared the extermination camps, he (Ahmadinejad) wants a (nuclear) bomb for what he says are 'civilian needs'," said Peres.

"We know perfectly well what his real intentions are and that's why we must take his declarations so seriously."

Iran announced earlier this month that scientists had successfully enriched uranium to make nuclear fuel although it insists its programme is designed only to meet energy needs.

Israel, itself the only Middle East state believed to possess nuclear weapons, is convinced that the real intention is to develop the bomb.

President Moshe Katsav may have held back from mentioning Iran by name but there was little doubt about the target of his address at Yad Vashem on Monday night.

"The free world must not stay idle in the face of countries which call for the destruction of Israel and want to possess a nuclear weapon," he said.

Defence Minister Shaul Mofaz had said earlier in the day that Ahmadinejad was "one the world's most dangerous leaders since Hitler" and that Israel was now facing an existential threat from Iran.

Many analysts drew similar comparisons, noting that Ahmadinejad's latest anti-Israel diatribe on Monday, when he said that the "fake" Jewish state "cannot survive", came on the eve of Holocaust memorial day.

"Now, more than ever, it seems that the chances of a new type of Holocaust, in the framework of which the Jews and humanity as we know it will be destroyed, is a palpable possibility," said Robert S. Witrich, head of the international anti-Semitism study centre at Jerusalem's Hebrew University.

"The threats made by Ahmadinejad, the jihad against the West and the fanatical anti-Semitism that permeates radical Islam, are palpable examples of this threat," he wroted in the top-selling Yediot Aharonot newspaper.