United Nations, Reuters—Israeli Prime Minister Benjamin Netanyahu on Tuesday dismissed a charm offensive by Iran’s new president as a ruse concocted by a “wolf in sheep’s clothing,” and declared that Israel was ready to stand alone to deny Tehran an atomic weapon.

In a combative address to the UN General Assembly, Netanyahu assailed the trustworthiness of Hassan Rouhani, Iran’s centrist president who has made diplomatic overtures to the United States and spoke by telephone last week with President Barack Obama.

“Rouhani doesn’t sound like Ahmadinejad,” Netanyahu said, referring to Rouhani’s hardline predecessor, Mahmoud Ahmadinejad, whose annual UN addresses were stridently anti-Western and anti-Israel.

“But when it comes to Iran’s nuclear weapons program, the only difference between them is this: Ahmadinejad was a wolf in wolf’s clothing, Rouhani is a wolf in sheep’s clothing, a wolf who thinks he can pull the wool over the eyes of the international community,” Netanyahu said.

“This is a ruse,” Netanyahu added. “It’s a ploy.”

Netanyahu’s address, the last at this year’s gathering of world leaders in New York, reflected Israeli worries that the emerging signs of what could become a US-Iranian rapprochement might lead to a premature easing of international sanctions and military threats designed to deny Iran the means to make a bomb.

“Don’t let up the pressure,” Netanyahu said, adding that the only deal that could be made with Rouhani was one that “fully dismantles Iran’s nuclear weapons program.”

Asked about Netanyahu’s speech, White House spokesman Jay Carney said Israel’s “skepticism is understandable.”

“After all, this is a country whose leadership until recently was pledging to annihilate Israel,” he said, referring to Ahmadinejad’s suggestions that Israel had no right to exist.

The United States, Israel and other countries accuse Iran of using its nuclear program to try to develop the capability to produce weapons. Iran says the program is for peaceful energy purposes only. During his General Assembly speech last week, Rouhani said nuclear weapons “have no place in Iran’s security and defense doctrine, and contradict our fundamental religious and ethical convictions.”

The Israeli leader referred to Rouhani’s 1989-2003 tenure as the head of Iran’s Supreme National Security Council, a time when he said Iranian “henchmen” killed opposition leaders in Berlin, 85 people at a Jewish center in Buenos Aires and 19 US soldiers in a bomb attack on the Khobar Towers in Saudi Arabia.

“Are we to believe that Rouhani, the national security adviser of Iran at the time, knew nothing about these attacks?” Netanyahu said. “Of course he did, just as 30 years ago Iran’s security chiefs knew about the bombings in Beirut that killed 241 American Marines and 58 French paratroopers.”

Netanyahu made clear that Israel, believed to possess the Middle East’s only atomic arsenal, was prepared to resort to unilateral military action against Iran if it deems diplomacy a dead end.

“I want there to be no confusion on this point. Israel will not allow Iran to get nuclear weapons. If Israel is forced to stand alone, Israel will stand alone. Yet in standing alone, Israel will know that we will be defending many, many others,” Netanyahu said.

The bulk of his speech was about Iran, but he also touched on the Israeli-Palestinian peace process, saying the Jewish state was prepared to make a “historic compromise.” He faulted Palestinian leaders for not reciprocating enough.

Rouhani, who took office last month after being elected in June, projected a more moderate tone from Iran at the world forum last week, with long-term adversaries Iran and the United States now preparing for renewed nuclear talks.

Later this month, Iran will meet with the five permanent UN Security Council members and Germany in Geneva to pick up from last week’s discussions in New York that included Iranian Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry.

Iran has made clear it wants a swift deal that would lift the crippling international sanctions against it and put an end to the decade-long standoff over its nuclear ambitions.

In a response to Netanyahu’s speech, Khodadad Seifi, a representative of the Iranian UN delegation, rejected Israel’s allegations and told the 193-nation General Assembly that Iran was “fully committed” to its nuclear nonproliferation obligations.

He warned Israel that Iran was able to respond to any Israeli attack, saying, “The Israeli prime minister had better not even think about attacking Iran, let alone planning for that.”

Netanyahu said Iran’s nuclear program had continued at a “vast and feverish” pace since the election of Rouhani.

“Like everyone else, I wish we could believe Rouhani’s words, but we must focus on Iran’s action,” Netanyahu said, adding that sanctions should be tightened if the Iranians pursue nuclear projects while negotiating with world powers.

At last year’s UN General Assembly, Netanyahu made headlines when he used a marker to draw Israel’s “red line” across a cartoonish bomb he displayed as a visual aid during his speech to illustrate advances in Iranian uranium enrichment.

“Iran has been very careful not to cross that line, but Iran is positioning itself to race across that line in the future at a time of its choosing,” he said. “Iran wants to be in a position to rush forward to build nuclear bombs before the international community can detect it and much less prevent it.”

Although Iran did not cross that “red line”, Israel worries that it has improved its technologies and is now capable of dashing toward a first bomb within weeks. On Tuesday, Netanyahu noted the Iranian heavy water plant Arak that, he said, could produce plutonium—another potential fuel for nuclear weapons.

If there are any changes taking place in Iran, Netanyahu said, it was the result of pressure on the Islamic Republic.

“I have argued for many years, including on this podium, that the only way to peacefully prevent Iran from developing nuclear weapons is to combine tough sanctions with a credible military threat. And that policy today is bearing fruit.”

Referring to the 1979 Islamic revolution in Iran, Netanyahu said: “Since that time, presidents of Iran have come and gone. Some presidents were considered moderates, others hardliners.”

“But they have all served that same unforgiving creed, that same unforgiving regime, that creed that is espoused and enforced by the real power in Iran, the dictator known as the supreme leader, first Ayatollah (Ruholla) Khomeini and now Ayatollah (Ali) Khamenei,” he said.

“President Rouhani, like the presidents who came before him, is a loyal servant of the regime,” Netanyahu added.

Netanyahu also noted the thousands of years of Persian-Jewish amity that ended with the fierce anti-Israel hostility ushered in by the 1979 revolution in Iran.

After meeting with Netanyahu on Monday, Obama reiterated his determination to prevent Iran from getting nuclear arms. Both leaders said their countries were cooperating on the issue.