The Obama administration was so certain that its forces were about to attack Syria in the chemical weapons crisis at the end of August, that US officials telephoned Israel’s prime minister and defense minister to give them “advance warning” the attack was about to take place.

The phone calls, Israel’s Channel 2 news revealed Friday, were made shortly after Secretary of State John Kerry on August 31 had accused Bashar Assad’s regime of an August 21 chemical weapons attack that killed 1,429 Syrians. Israel’s leaders were told explicitly that the US would be taking punitive military action against the Assad regime within 24-48 hours.

The calls were made in accordance with the US promise to give Israel a warning ahead of such an attack, so that it could take steps to defend itself against any potential Syrian retaliation that might target the Jewish state.

Prime Minister Benjamin Netanyahu and his Defense Minister Moshe Ya’alon were personally telephoned, the TV report said, without revealing who made the calls.

In fact, however, President Barack Obama, a day later on September 1, surprisingly announced that he would seek Congressional authorization before a strike on Syria. (Israel was given advance warning of that change of tack as well, some four hours before the president’s announcement.) Ultimately Obama did not carry out the narrow, punitive action he had said he was planning, instead joining a Russian-led initiative for a diplomatic solution aimed at stripping Assad of his chemical weapons.

The TV report indicated that Obama’s volte face that weekend — having sent Kerry to deliver an impassioned address in which the secretary said that the “thug and murderer” Assad had to be held accountable for gassing his own people — has cast doubts in Israel as to the credibility of any last-resort American military threat against Iran. Kerry had noted in his speech, before the president’s change of heart, that the world was watching “to see whether the United States and our friends mean what we say [about not tolerating chemical weapons use]. It is directly related to our credibility and whether countries still believe the United States when it says something.”

A close colleague of Netanyahu’s, Likud MK Tzachi Hanegbi, made that Israeli concern explicit in an interview with The Times of Israel earlier this week. Hanegbi indicated that Israel is no longer certain that the Obama administration would employ military force even as a last resort to thwart Iran attaining nuclear weapons.

That new uncertainty was a direct consequence of the Syrian chemical weapons crisis, he made clear. And it explained why Netanyahu, in his speech at the UN General Assembly on Tuesday, felt the imperative to warn the Iranians that Israel would act on its own if necessary.

Speaking immediately after Netanyahu’s speech, Hanegbi stressed that “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.”

Explaining why Netanyahu had made that threat, Hanegbi said Israel’s 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.

“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.’”