NEW YORK — Israel is no longer certain that the Obama administration would employ military force even as a last resort to thwart Iran attaining nuclear weapons, a senior colleague of Prime Minister Benjamin Netanyahu indicated for the first time.

That new uncertainty was a relatively recent development, Tzachi Hanegbi, a Likud Knesset member and former cabinet minister, further indicated. The turning point was America’s response to the crisis over the alleged use of chemical weapons by Syria’s Assad regime in late August. And it explained why Netanyahu, in his speech at the UN General Assembly, felt the imperative to warn the Iranians that Israel would act on its own if necessary.

Speaking to The Times of Israel in New York in the wake of Netanyahu’s speech to the UN General Assembly on Tuesday, Hanegbi said “the most dramatic part” of the prime minister’s address was the passage in which he warned, “Israel will not allow Iran to get nuclear weapons. If Israel is forced to stand alone, Israel will stand alone.”

Why was this so dramatic, Hanegbi asked rhetorically? “Because it marked the first time it was said in public, and not behind closed doors, that Israel will act even if stands alone.”

“What does that mean, to ‘stand alone,’” he asked, again rhetorically? “After all, we didn’t expect the world to act. But our expectation was and remains that the United States — if the negotiations do indeed fail — would employ the military option which the president has said several times is not removed from the table. But we saw recently that even if the president has a clear and unequivocal position, as in the Syrian case, sometimes all kinds of constraints are placed upon him that are not under his control, like the position of Congress or American public opinion. (President Barack Obama initially threatened punitive military action for the Assad regime’s August 21 alleged chemical weapons attack, later said he would consult Congress, and ultimately accepted a Russian-instigated diplomatic initiative.)

“Therefore,” Hanegbi went on, “the prime minister essentially is telling the Iranians: ‘Do not delude yourselves. Even if the Americans will be prevented from acting against you, we will know how to defend ourselves, with our own forces.'”

Asked whether, rhetoric aside, Israel could actually strike at Iran when the US president was engaged with Tehran in a diplomatic effort to resolve the nuclear crisis, Hanegbi dismissed such a scenario. “The non-diplomatic option will only become applicable once it is clear that the diplomatic option failed,” he said. “Since the American president clarified what he expects in the diplomatic realm, it is clear that if this doesn’t work, he couldn’t come and complain to any other player.”

Hwoever, a senior official in the prime minister’s delegation to the US told The Times of Israel Wednesday that a preemptive Israeli strike against Iranian nuclear facilities remains a viable option even while Washington is engaged in a diplomatic process with Tehran.

“The prime minister was very clear about it. He said that that option is still on the table,” said the official, who spoke on condition of anonymity. “It is not the preferred option, as we prefer a successful solution to the crisis through diplomatic means, but it’s always on the table.”

In his comments to The Times of Israel, Hanegbi added that “the prime minister’s position represents the State of Israel, and he is very skeptical about Iran’s willingness to give up on a dream they have tried to advance for more than 15 years.”

Hanegbi, who is considered close to the prime minister, also noted that Netanyahu’s speech included a “hardening of positions” regarding Jerusalem’s demands of Iran, as for the first time he required that Iran close its uranium enrichment plant in Natanz, as well as its facilities at Qom and Arak.

Any “meaningful” diplomatic solution to the Iranian nuclear standoff would require four steps, Netanyahu told the UN: “First, cease all uranium enrichment… Second, remove from Iran’s territory the stockpiles of enriched uranium. Third, dismantle the infrastructure for nuclear breakout capability, including the underground facility at Qom and the advanced centrifuges in Natanz. And, four, stop all work at the heavy water reactor in Arak aimed at the production of plutonium.”

Previously, his four stated conditions had included closure of the Qom and Arak facilities, but Tuesday’s speech for the first time included the demand to close Natanz as well. “Apparently, what can be done in Qom can also be done in all other facilities,” said Hanegbi.

Netanyahu on Wednesday morning spoke to presidents and directors of leading media companies, staffers said. In his counter-Rouhani media blitz, he was later giving interviews to NBC, CBS and Univision (Spanish). On Thursday, he was to speak to CNN, ABC, and others, before heading home.