Israeli prime minister Benjamin Netanyahu will tomorrow try to foil Iran’s moves towards rehabilitation in the international community during a speech at the UN General Assembly aimed at reversing the diplomatic and public opinion gains made by the new Iranian president Hassan Rouhani.

In remarks late on Saturday before departing for the United States, where he will meet US President Barack Obama later today, Mr Netanyahu signalled that as far as Israel is concerned, nothing has changed but the rhetoric from the years of President Mahmoud Ahmadinejad, who denied the Holocaust and spoke of Israel’s removal. Above all, Mr Netanyahu will stress that Iran is still intent on attaining a nuclear bomb, something Israel views as an existential threat.

“I will tell the truth in the face of the sweet talk and the blitz of smiles. One must speak facts and one must tell the truth,” Mr. Netanyahu said.

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In his own UN speech last week, Mr Rouhani last week departed from Mr Ahmadinejad’s rhetoric and acknowledged suffering of Jews during the Holocaust although he made clear in separate remarks that he did not view Nazi crimes as justification for dispossession of the Palestinians.

A phone call Friday between Mr Obama and Mr Rouhani, the first contact between presidents of the two nations since 1979, elicited no official Israeli reaction but for some raised the prospect that the Jewish state, which pulled its diplomats out of the General Assembly to boycott Mr Rouhani’s speech, could eventually become isolated in its continued espousal of unrelenting pressure on Iran, including the threat of military action.

Still, Zalman Shoval, former Israeli ambassador to the US said “We don’t think that at this point the US is being fooled.

“Israel doesn’t want to be the odd man out but doesn’t mind being the one to point to the facts as they are,” he added. “Churchill was called a war-monger in the 1930s but at the end of the day he was right.”

Mr Netanyahu’s closest ally, Avigdor Lieberman, the chairman of the Knesset Foreign Affairs and Defence Committee, hinted yesterday that Israel would act alone militarily to destroy Iranian nuclear capabilities if necessary. “It is worth remembering that with the Iraqi reactor Israel was alone and sounded the alarm,” he wrote on his Facebook page, referring to the 1981 strike on Iraq’s Osirak nuclear reactor. “In retrospect it became clear we were right.”

“The conciliation offensive of Rouhani is no more than an additional fraudulent exercise like the one North Korea did in its time,” Lieberman added.

Mr Netanyahu has said that Iran needs to take four steps to show it is serious about stopping what Israel believes is its drive to a bomb: halt all uranium enrichment, transfer the enriched uranium it has out of Iran, close the Fordow enrichment facility and halt work on a plutonium channel to a nuclear weapon.

Meanwhile, the Shin Bet internal security agency, which is run by the prime minister’s office, yesterday said it is holding an Iranian with Belgian nationality on suspicion he spied in Israel on behalf of Iran’s elite revolutionary guards, including taking pictures of the American embassy in Tel Aviv.

The Shin Bet stressed that the man, who it identified as Ali Mansuri, 55, had joined a unit responsible for terrorist attacks in sites throughout the world. It said he had entered Israel under the name Alex Mans to set up business ventures as a cover for Iranian intelligence activity.

He was arrested at Ben Gurion Airport on 11 September. The agency said he had photographed the US embassy in order to “follow” activity there.

Israel Radio quoted officials in Mr Netanyahu’s entourage in the US as saying the arrest “is further proof that the words coming from Iran do not match the criminal actions it undertakes”. But lawyers appointed by the state to defend Mr Mansuri were quoted by Israel’s Ynet news agency as saying he was “a businessman who is not motivated by an anti-Israel or pro-Iranian agenda.” They said Mr Mansuri was prevented from seeing lawyers for more than a week.

Zahava Galon, head of the liberal Meretz party, yesterday voiced support for the American-Iranian contacts. “I think that cautious contacts between the US and Iran are the correct and necessary step. If there is any way to prevent Iran going nuclear without another war we have a moral obligation to realise it.”