JERUSALEM, Israel -- Israeli Prime Minister Benjamin Netanyahu will be one of the last speakers at this year's United Nations General Assembly meeting.
Netanyahu faces a daunting challenge. His speech will be one of his most important on the world stage.
While Iran is launching a charm offensive, the Israeli prime minister will try once more to warn the world about the dangers of a nuclear Iran.
"He faces, I would say, probably the biggest diplomatic challenge that I can remember," former Israeli Ambassador to the U.S. Danny Ayalon told CBN News.
Ayalon said Netanyahu will confront a skeptical audience after Iranian President Hassan Rouhani's charm offensive to convince the West that Iran doesn't want to build a nuclear bomb and the economic sanctions should be lifted.
"The challenge is not from the sweet talk, the charm offensive of the Iranians. It's the response from the international community," Ayalon explained. "How easily they have been embracing the Iranians without calling them into check."
"So this is the main challenge -- to tell the world the truth, to set the record straight and keep the pressure on Iran," he said.
Before his U.N. speech, Netanyahu met with President Barack Obama. His main topic: Iran. Obama said he's willing to talk with the Islamic Republic.
"What I also shared with the prime minister is that because of the extraordinary sanctions that we have been able to put in place over the last several years, the Iranians are now prepared, it appears, to negotiate," the president said. "We have to test diplomacy."
Netanyahu said he wants to see action, not just talk.
"We have a saying in Hebrew…you would say it in English, 'What's the bottom line?' And the bottom line again is that Iran fully dismantles its military nuclear program."
As Netanyahu prepares to address the U.N. General Assembly, many Israelis remain skeptical about Iran's intentions and the decision by the White House to negotiate an end to Iran's nuclear program.
In the meantime, the momentum for diplomacy is building. U.S. Secretary of State John Kerry now says he feels a deal with Iran about its nuclear program could be finished within three to six months.