Israel voiced concern on Tuesday over a potential meeting of the US and Iranian presidents, saying Tehran sought reconciliation with world powers as a ruse to press on with its nuclear programme.
Iran's new government has taken its charm offensive to the annual UN General Assembly, agreeing to international nuclear negotiations that would include its foreign minister seeing US secretary of state John Kerry.
US officials also said a meeting was possible this week between President Barack Obama and Iranian counterpart Hassan Rouhani - a landmark after more than three decades of hostility.
Israel sees a mortal menace in an Iranian bomb it says could be months away from production and says may now be expedited should world powers back off sanctions and readiness for a war of last-resort against Tehran.
Iran has rejected several UN Security Council resolutions aimed at curbing its nuclear projects with bomb-making potential, insisting the programme is entirely peaceful.
It has also tried to shift scrutiny to Israel's assumed atomic arsenal.
Asked if there would be an Obama-Rouhani handshake, Yuval Steinitz, the cabinet minister representing Israel at the UN forum in New York, said: "I hope not. I don't know."
"But really the important thing is not just words and appearances. The important thing is the actions. The important thing is the resolutions," Steinitz told Israel's Army Radio.
"And I really hope that the whole world, and chiefly among them the United States, will say, 'Okay, it's nice to hear the smiles, the new rhetoric, but as long as you don't change the conduct, and as long as you don't make a real concession in the nuclear project, the economic sanctions will continue and if there is need, will be joined by a military threat as well'."
In contrast to confrontational former President Mahmoud Ahmadinejad, Rouhani favours restrained outreach, saying on Monday he would "present the true face of Iran as a cultured and peace-loving country" at the United Nations.
Rouhani and Obama were scheduled to deliver speeches to the General Assembly on Tuesday.
Washington says it remains determined to deny the Iranians the means to make nuclear arms but its willingness to engage them directly complicates strategy for Israeli Prime Minister Benjamin Netanyahu, who will address the world forum on October 1.
The day before, Netanyahu is scheduled to meet Obama at the White House for discussions on Iran that Israeli officials say will affect the content and tone of his UN speech.
At last year's speech, Netanyahu set a "red line" that he said would trigger Israeli military strikes on Iranian nuclear sites, drawing it across a cartoonish bomb representing the pace and scale of the Islamic Republic's uranium enrichment.
This time around, some Israeli officials predict, he will opt for a more sober message, with facts trumping rhetoric.
As Iran has kept its uranium enrichment below the Israeli threshold, they said, he will note it has also made progress on another track that could yield bomb-grade plutonium.
Steinitz said last week that Iran, on its current course,could make a nuclear weapon in six months.
"There is no more time" for nuclear negotiations, he told the Israel Hayom daily. But with a new round of such talks in the works, Steinitz reaffirmed Israel's position that it would support a diplomatic solution that truly halted Iran's nuclear programme.
He described this as unlikely, saying Rouhani brought a deceptive change of style but not substance to Iranian policymaking.
"We are certainly warning the entire international community that Iran may want an agreement, but it is liable to be the Munich agreement," Steinitz said, referring to the 1938 appeasement of Nazi Germany.
"Rouhani wants to hoodwink, and some in the world want to be hoodwinked, and the role of little Israel is to explain the truth and to stand in the breach. And that is what we are doing to the best of our abilities. It is a long struggle."