Israeli Prime Minister Benjamin Netanyahu has travelled to the United States with a simple message for Barack Obama and the United Nations: "Don't be fooled by Iran's new leadership."
Netanyahu fears the world is being taken in by the nuclear-ambitious country's "sweet talk" and recent conciliatory gestures.
He insists Tehran is using them as a smokescreen to conceal an unabated march towards a nuclear bomb.In White House talks with Obama yesterday, Netanyahu warned Iran must dismantle its "military nuclear programme" as a condition for a diplomatic breakthrough that would head off the prospect of military action.
Netanyahu told Obama that such a step was Israel's "bottom line" as hopes rise of a deal to end the nuclear showdown between Washington, world powers and Tehran.
Netanyahu warned that Iran was committed to Israel's destruction and that its words and actions should be judged with that in mind.
"The bottom line is that Iran fully dismantles its military nuclear programme," he said after over an hour of talks with Obama in the Oval Office.
Netanyahu also argued that economic sanctions must be kept in force through any diplomatic process with Iran, which will resume next month in Geneva.
"In fact, if Iran continues to advance its nuclear programme during negotiations, the sanctions should be strengthened."
Similarly, in his speech at the UN today , Netanyahu "will make it very clear that Israel and the world at large should continue to be on guard", he said.
Obama assured Netanyahu that he would be "clear eyed" in talks with Iran.
"We take no options off the table, including military options," Obama said, adding that words were not sufficient for Iran to resolve concerns about its nuclear program.
However, Obama admitted that Iran seemed ready to negotiate.
"We have to test diplomacy, we have to see if in fact they are serious about their willingness to abide by international norms and international law," Obama said.
Israeli leaders watched with great dismay what they derisively called the "smiley campaign" by Iran's new president, Hassan Rowhani, last week.
Rowhani delivered a conciliatory speech at the UN in which he repeated Iran's official position that it has no intention of building a nuclear weapon.
He also declared his readiness for new talks with the West.
Capping off the visit, Rowhani and Obama held a 15-minute telephone call as the Iranian leader was travelling to the airport.
By the end of the call - the first conversation between the two nations' leaders in 34 years - Obama was suggesting that a breakthrough on the nuclear issue could even lead to the development of new ties.
US and European diplomats hailed a "very significant shift" in Iran's attitude and tone. But for Netanyahu, such sentiments are nothing short of a nightmare.
Rowhani also faced criticism back home in Iran, where the head of the elite Revolutionary Guards force said the telephone call with Obama came too soon.
The comments by General Mohammad Ali Jafari were the first public criticism of the move by a senior official.
"The president took a firm and appropriate position during his stay" in New York for the United Nations General Assembly, Jafari said in an interview with the Tasnimnews.com  website.
"But just as he refused to meet Obama, he should also have refused to speak with him on the telephone and should have waited for concrete action by the United States."
For years, Netanyahu has warned Iran is marching towards the development of nuclear weapons.
It is an assessment widely shared by the West because of Iran's continued enrichment of uranium and its run-ins with international nuclear inspectors.
Israel also has a long list of other grievances against Iran, citing its support for hostile Arab militant groups, its development of long-range missiles and alleged Iranian involvement in attacks on Israeli targets in Europe and Asia.
Additional reporting by Agence France-Presse