TEL AVIV — As Israel braces for an attack from Iran — fueling fighter jets, positioning air defense batteries and coordinating with Washington on the placement of U.S. military assets — there is growing apprehension about one of its most critical lines of defense: an American-led Arab coalition that helped thwart the last Iranian assault.

The once covert alliance, involving Jordan, Saudi Arabia and the United Arab Emirates, burst into public view on the night of April 13, when it aided Israel in intercepting 99% of more than 300 drones and missiles launched from Iran — the first direct strike of its kind by Tehran after decades of shadow war with the Jewish state.

Israel’s military chief lauded the collaboration at the time as paving the way for “new opportunities for cooperation in the Middle East.” White House national security adviser John Kirby said it sent “a strong message about where Israel is in the region versus where Iran is in the region.”

Four months later, with Iran vowing to respond forcefully to the assassination of Hamas leader Ismail Haniyeh in its own backyard, Israel is more regionally isolated, which military analysts say could make the country more vulnerable. There are also fears that, even with American support, Israel’s aerial defense systems may not be able to fully counter a massive, coordinated attack.

Prime Minister Benjamin Netanyahu has refused to agree to a cease-fire and hostage release deal in Gaza, despite pressure from Washington and appeals from his own military chiefs. The killing of Haniyeh — the lead Hamas negotiator — angered U.S. officials and Arab leaders, who had believed talks were at a critical stage. While Israel has neither confirmed nor denied its role in the assassination, it told U.S. officials immediately afterward that it was responsible.

Even in April, Arab countries downplayed their roles in staving off the Iranian attack, wary of retaliation from Tehran and not wanting to be seen as supportive of Israel at a time of widespread public fury over the human toll of the Gaza war. Those concerns are even more pronounced now, and Arab states have sought to publicly distance themselves from any involvement in the next round of violence.

Jordan and Saudi Arabia have declared they do not want their airspace transformed into a battle zone. Egypt has said it would not “take part in a military axis that would participate in repelling” an Iranian attack.

Such public statements are “very disturbing,” according to a senior Israeli politician who helped build the regional coalition, speaking on the condition of anonymity to discuss sensitive security matters. While the Arab states in missile range want Iran contained, he said, the ties that bind them to Israel are delicate and have only been tested once before on a large scale.

Facing down the prospect of all-out war, “Israel is operating quite alone,” he acknowledged.

“We’re working really, really hard, with intense diplomacy, to try to avoid an escalation,” Kirby told reporters on Wednesday, while adding that President Joe Biden “ordered additional military resources to the region to make sure that, should Israel be attacked, that the United States can ably come to her defense.”

Iran’s attack in April, launched after an Israeli strike near a diplomatic facility in Damascus, was well choreographed, giving Israel and its allies valuable time to prepare. Officials believe the assault this time could be more sudden, larger in scale and longer — possibly lasting several days instead of several hours. It could also be a coordinated barrage from multiple directions, involving Iranian proxies in Iraq, Yemen, Syria and Lebanon.

Over the past 10 months, Hezbollah militants in Lebanon have used low-flying, high-speed explosive drones to hit military sites and private homes in Israel — eluding the country’s vaunted aerial defense systems, which are designed to identify and intercept more traditional rockets that fly at higher altitudes and along linear flight paths. Such drones could pose a significant danger if unleashed in large numbers, weapons experts say.

“Our response is coming and it will be strong, impactful and effective,” Hezbollah leader Hasan Nasrallah said in a speech on Wednesday.

The group could also make use of longer-range munitions that it claims to possess but has never publicly displayed. Repelling such a barrage would probably come at a high price for Israel: Iron Dome interceptions cost around $30,000 per interception; the Arrow 3, designed to down ballistic missiles, runs an estimated $3 million per interception.

Israel assesses that Hezbollah will start the attack, potentially firing toward Tel Aviv and using guided missiles, according to Yoel Guzansky, a former official on Israel’s National Security Council who is now a senior researcher at the Institute for National Security Studies in Tel Aviv.

A worst-case scenario, he said, would be a multi-front attack from other Iranian proxies designed to “challenge the limits of Israel’s systems, which can be overwhelmed … and which, as seen in April, rely on the regional coalition for strategic depth.”

Guzansky said Israel has communicated to Hezbollah and Iran that hitting civilian population centers would be a red line and would elicit a forceful response.

“If Hezbollah continues its aggression, Israel will fight it, with all its might,” Defense Minister Yoav Gallant warned in a message in Arabic posted on X on Thursday. “He who plays with fire may expect destruction.”

Israel might also consider a preemptive attack against Iran if it concluded an attack was imminent, Israeli media reported Monday after Netanyahu met with his defense chiefs. “That’s something that we haven’t gotten to yet, but the future is yet to come,” the senior Israeli politician said.

Gen. Michael E. Kurilla, head of U.S. Central Command, was in Israel for a second time this week to discuss military coordination. Newly deployed U.S. assets include a squadron of F-22 Raptors, naval cruisers and destroyers, and the aircraft carrier USS Abraham Lincoln and its accompanying ships, which are heading toward the Middle East to replace another carrier strike group that will be departing the region.

“The U.S. is much busier than it was in April, but it also realizes that a regional war will affect the economy, and it is in their interest to stop the escalation,” said Israel Ziv, a retired major general who served as the head of the Israel Defense Forces Operations Division.

But he urged Israeli leaders not to take American support for granted: “Here, I think Israel could make a mistake, in going to a regional war with the assumption that its assets will always be there.”

He also predicted Israel would encounter difficulties in keepings its regional coalition together, “since they’re not all ready to work with Netanyahu.”

Abdullah Al-Junaid, a political analyst in Bahrain, said that Persian Gulf states were still invested in partnering with Israel to contain Iran, but that any long-term alliance would require progress toward a resolution between Israel and the Palestinians — which Netanyahu and his far-right allies have refused to consider. Their intransigence has stalled U.S.-backed efforts to expand normalization agreements between Israel and its Arab neighbors, including Saudi Arabia.

The current regional conflict “is empowering the extremist models that Iran represents,” Junaid said, which “is in no one’s interest.”

“Now we need to dig deeper and find out a Middle East 2.0,” he said. “The alternative is not sustainable.”

Lior Soroka in Tel Aviv, Missy Ryan in Jerusalem and Dan Lamothe in Washington contributed to this report.