In one of his first forays into foreign policy since taking over from the coma-stricken Prime Minister Ariel Sharon, Olmert also said he believed a diplomatic solution was possible before Iran was able to obtain nuclear weapons.

"Israel cannot allow in any way or at any stage someone who has such hostile intentions against us to obtain weapons that could threaten our existence," Olmert said in talks with President Moshe Katsav.

Israel has come to view the Islamic republic as its number one enemy and its fears were heightened when President Mahmoud Ahmadinejad in October called for the Jewish state to be "wiped off the map."

Army chief Dan Halutz said the possibility of Iran obtaining nuclear weapons was "the sole existential threat facing the state of Israel."

"I suggest that Israel should not consider that this man is crazy. We must take him seriously," he said in an address at Haifa University.

Israel itself is believed to be the only nuclear power in the Middle East, although it has never admitted to having a non-conventional arsenal.

Iran faces the threat of being referred to the UN Security Council for resuming nuclear fuel research work that Israel and the Western powers fear would give the regime the know-how to build a bomb.

Tehran insists such work is legal given it has signed the nuclear Non-Proliferation Treaty and has branded atomic weapons "un-Islamic".

Olmert said concerted international pressure could still bring about a diplomatic solution.

"I believe that there is a way to prevent non-conventional weapons coming into the hands of those who pose a danger to the entire world," Olmert said.

"The Iranian issue is at the top of the agenda for the Israeli government as well as the international community.

"It is being dealt within a continuous manner with contacts between the government and those in Europe and the United States."

A source in the prime minister's office said the trip by the Moscow-bound delegation, which includes national security advisor Giora Eiland and the head of Israel's atomic energy commission Gideon Frank, would "enable an exchange of views and information on the state of play with Iran's nuclear programme."

President Vladimir Putin's government, one of the five permanent members of the Security Council, has offered to enrich uranium for Iran in Russia in a move designed to allay international concern over Tehran's nuclear ambitions.

Moscow enjoys close ties with the Iranian leadership and is building Iran's first nuclear power station at Bushehr, but has voiced concern at Tehran's latest move.

Ephraim Kam, an analyst at Tel Aviv University's Jaffee Centre for Strategic Studies, said the Israeli government understands that Russia's stance is crucial in keeping Iran in check.

"Russia plays a key role in the nuclear programme, that's why Israel is trying to convince Moscow to toughen its position and adopt the firmer stance that we have seen from America and the Europeans.

"It also seems that Moscow is not against the sanctions that could be laid down by the Security Council but the real question is what kind of sanctions -- economic measures or merely symbolic?"

Moscow has so far held back from joining the clamour for punitive measures against Iran, with Foreign Minister Sergei Lavrov saying sanctions were "not the best and by no means the only way to resolve international problems.

Israeli officials have played down the idea of a pre-emptive strike against Iran's nuclear facilities but the outgoing head of military intelligence, Aharon Zeevi, said last month that such a move was "not impossible".

In 1981, Israel bombed Iraq's French-built Osirak nuclear reactor.

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