"It is very easy to receive a pat on the shoulder from the international community, to bow one's head," Netanyahu said at a candle-lighting ceremony in Rome's main synagogue which he visited with Letta.
"I would like to dispel any illusions. Iran aspires to attain an atomic bomb. It would thus threaten not only Israel but also Italy, Europe and the entire world," he was quoted as saying on his website.
"There should be no going astray after the attack of smiles. Today there is a regime in Iran that supports terrorism, facilitates the massacre of civilians in Syria and unceasingly arms its proxies," he said.
Netanyahu later today will be received for the first time at an audience by Pope Francis, who is expected to travel to the Middle East next year.
Israeli sources say the visit could take place before Israeli President Shimon Peres ends his term in July.
Although no date has been made official, sources on both sides say it is likely to take place on May 25-26.
Israel and the Vatican first established full diplomatic relations in 1993, but have been engaged in years of thorny diplomatic negotiations over property rights and tax exemptions for the Catholic Church, which have yet to be fully resolved.
Netanyahu and Francis are also expected to discuss negotiations between Israel and the Palestinians, which resumed in July after a three-year hiatus but have faltered due to Israeli plans for new settlement building.


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