TEL AVIV — In the initial sales pitch to Hezbollah two years ago, the new line of Apollo pagers seemed precisely suited to the needs of a militia group with a sprawling network of fighters and a hard-earned reputation for paranoia.

The AR924 pager was slightly bulky but rugged, built to survive battlefield conditions. It boasted a waterproof Taiwanese design and an oversized battery that could operate for months without charging. Best of all, there was no risk that the pagers could ever be tracked by Israel’s intelligence services. Hezbollah’s leaders were so impressed they bought 5,000 of them and began handing them out to mid-level fighters and support personnel in February.

None of the users suspected they were wearing an ingeniously crafted Israeli bomb. And even after thousands of the devices exploded in Lebanon and Syria, few appreciated the pagers’ most sinister feature: a two-step deencryption procedure that ensured most users would be holding the pager with both hands when it detonated.

As many as 3,000 Hezbollah officers and members — most of them rear-echelon figures — were killed or maimed, along with an unknown number of civilians, according to Israeli, U.S. and Middle Eastern officials, when Israel’s Mossad intelligence service triggered the devices remotely on Sept. 17.

As an act of spy craft, it is without parallel, one of the most successful and inventive penetrations of an enemy by an intelligence service in recent history. But key details of the operation — including how it was planned and carried out, and the controversy it engendered within Israel’s security establishment and among allies — are only now coming to light.

This account, including numerous new details about the operation, was pieced together from interviews with Israeli, Arab and U.S. security officials, politicians and diplomats briefed on the events, as well as Lebanese officials and people close to Hezbollah. They spoke on the condition of anonymity to discuss sensitive intelligence. They describe a years-long plan that originated at Mossad headquarters in Tel Aviv and ultimately involved a cast of operatives and unwitting accomplices in multiple countries. The Washington Post account reveals how the attack not only devastated Hezbollah’s leadership ranks but also emboldened Israel to target and kill Hezbollah’s top leader, Hasan Nasrallah, raising the risk of a wider Middle East war.

Iran launched around 180 missiles against Israel on Tuesday in retaliation for Israeli attacks on Hezbollah’s leadership and warned of harsher consequences if the conflict escalates.

“The resistance in the region will not back down even with the killing of its leaders,” Iranian Supreme Leader Ali Khamenei said during a Friday sermon in Tehran.

But in Israel, the strike convinced the country’s political leaders that Hezbollah could be put on the ropes, susceptible to a systematic dismantling using airstrikes and, eventually, a ground invasion. Yet while marveling at the plot’s success, some officials continue to worry about the broader ripples of the strike, in a conflict that continues to spiral.

One Israeli political official, referring to the pager plot, summed up the anxieties in a quip at a meeting with Mossad officials.

“We cannot make a strategic decision such as an escalation in Lebanon while counting on a toy,” the official said.

Designed by Mossad, assembled in Israel

The idea for the pager operation originated in 2022, according to the Israeli, Middle Eastern and U.S. officials familiar with the events. Parts of the plan began falling into place more than a year before Hamas’s Oct. 7 attack that put the region on a path to war. It was a time of relative quiet on Israel’s war-scarred northern border with Lebanon.

Among the half dozen Iranian-backed militia groups with weapons aimed at Israel, Hezbollah is by far the strongest. Israeli officials had watched with increasing anxiety as the Lebanese group added new weapons to an arsenal already capable of striking Israeli cities with tens of thousands of precision-guided missiles.

Mossad, the Israeli intelligence service responsible for combating foreign threats to the Jewish state, had worked for years to penetrate the group with electronic monitoring and human informants. Over time, Hezbollah leaders learned to worry about the group’s vulnerability to Israeli surveillance and hacking, fearing that even ordinary cellphones could be turned into Israeli-controlled eavesdropping and tracking devices.

Thus was born the idea of creating a kind of communications Trojan horse, the officials said. Hezbollah was looking for hack-proof electronic networks for relaying messages, and Mossad came up with a pair of ruses that would lead the militia group to purchase devices that seemed perfect for the job — equipment that Mossad designed and had assembled in Israel.

The first part of the plan, booby-trapped walkie-talkies, began being inserted into Lebanon by Mossad nearly a decade ago, in 2015. The mobile two-way radios contained oversized battery packs, a hidden explosive and a transmission system that gave Israel complete access to Hezbollah communications.

For nine years, the Israelis contented themselves with eavesdropping on Hezbollah, the officials said, while reserving the option to turn the walkie-talkies into bombs in a future crisis. But then came a new opportunity and a glitzy new product: a small pager equipped with a powerful explosive. In an irony that would not become clear for many months, Hezbollah would end up indirectly paying the Israelis for the tiny bombs that would kill or wound many of its operatives.

Because Hezbollah leaders were alert to possible sabotage, the pagers could not originate in Israel, the United States or any other Israeli ally. So, in 2023, the group began receiving solicitations for the bulk purchase of Taiwanese-branded Apollo pagers, a well-recognized trademark and product line with worldwide distribution and no discernible links to Israeli or Jewish interests. The Taiwanese company had no knowledge of the plan, officials said.

The sales pitch came from a marketing official trusted by Hezbollah with links to Apollo. The marketing official, a woman whose identity and nationality officials declined to reveal, was a former Middle East sales representative for the Taiwanese firm who had established her own company and acquired a license to sell a line of pagers that bore the Apollo brand. Some time in 2023, she offered Hezbollah a deal on one of the products her firm sold: the rugged and reliable AR924.

“She was the one in touch with Hezbollah, and explained to them why the bigger pager with the larger battery was better than the original model,” said an Israeli official briefed on details of the operation. One of the main selling points about the AR924 was that it was “possible to charge with a cable. And the batteries were longer lasting,” the official said.

As it turned out, the actual production of the devices was outsourced and the marketing official had no knowledge of the operation and was unaware that the pagers were physically assembled in Israel under Mossad oversight, officials said. Mossad’s pagers, each weighing less than three ounces, included a unique feature: a battery pack that concealed a tiny amount of a powerful explosive, according to the officials familiar with the plot.

In a feat of engineering, the bomb component was so carefully hidden as to be virtually undetectable, even if the device was taken apart, the officials said. Israeli officials believe that Hezbollah did disassemble some of the pagers and may have even X-rayed them.

Also invisible was Mossad’s remote access to the devices. An electronic signal from the intelligence service could trigger the explosion of thousands of the devices at once. But, to ensure maximum damage, the blast could also be triggered by a special two-step procedure required for viewing secure messages that had been encrypted.

“You had to push two buttons to read the message,” an official said. In practice, that meant using both hands.

In the ensuing explosion, the users would almost certainly “wound both their hands,” the official said, and thus “would be incapable to fight.”

An encrypted message

Most top elected officials in Israel were unaware of the capability until Sept. 12. That’s the day Prime Minister Benjamin Netanyahu summoned his intelligence advisers for a meeting to discuss potential action against Hezbollah, Israeli officials said.

According to a summary of the meeting weeks later by officials briefed on the event, Mossad officials offered a first glimpse into what had been one of the agency’s most secretive operations. By then, the Israelis had placed booby-trapped pagers in the hands and pockets of thousands of Hezbollah operatives.

Intelligence officials also talked about a long-held anxiety: With the escalating crisis in southern Lebanon, there was a growing risk the explosives would be discovered. Years of careful planning and deception could quickly come to naught.

Across Israel’s security establishment, an intense debate erupted, officials said. Everyone, including Netanyahu, recognized that the thousands of exploding pagers could do untold damage to Hezbollah, but could also trigger a fierce response, including a massive retaliatory missile strike by surviving Hezbollah leaders, with Iran possibly joining in the fray.

“It was clear that there were some risks,” an Israeli official said. Some, including senior Israel Defense Forces officials, warned of the potential for a full-fledged escalation with Hezbollah, even as Israeli soldiers were continuing operations against Hamas in Gaza. But others, chiefly Mossad, saw an opportunity to disrupt the status quo with “something more intense.”

The United States, Israel’s closest ally, was not informed of the booby-trapped pagers or the internal debate over whether to trigger them, U.S. officials said.

Ultimately, Netanyahu approved triggering the devices while they could inflict maximum damage. Over the following week, Mossad began preparations for detonating both the pagers and walkie-talkies already in circulation.

In Jerusalem and Tel Aviv, meanwhile, the debate over the Hezbollah campaign expanded to include another profoundly consequential target: Nasrallah himself.

Mossad had known of the leader’s whereabouts in Lebanon for years and tracked his movements closely, officials said. Yet the Israelis held their fire, certain that an assassination would lead to all-out war with the militia group, and perhaps with Iran as well. American diplomats had been pressing Nasrallah to agree to a separate cease-fire with Israel, without links to the fighting in Gaza, hoping for a deal that could lead to the withdrawal of Hezbollah fighters from the southern Lebanese bases that threatened Israeli citizens in communities near the border.

Senior Israeli officials said they voiced support for the cease-fire proposal, but Nasrallah withheld his consent, insisting on a cease-fire for Gaza first, U.S. and Middle Eastern officials said. Some senior political and military officials in Israel remained deeply uncertain about targeting Nasrallah, fearing the fallout in the region.

On Sept. 17, even as the debate in Israel’s highest national security circles about whether to strike the Hezbollah leader raged on, thousands of Apollo-branded pagers rang or vibrated at once, all across Lebanon and Syria. A short sentence in Arabic appeared on the screen: “You received an encrypted message,” it said.

Hezbollah operatives dutifully followed the instructions for checking coded messages, pressing two buttons. In houses and shops, in cars and on sidewalks, explosions ripped apart hands and blew away fingers. Less than a minute later, thousands of other pagers exploded by remote command, regardless of whether the user ever touched his device.

The following day, on Sept. 18, hundreds of walkie-talkies blew up in the same way, killing and maiming users and bystanders.

It was the first of a series of blows aimed at the heart of one of Israel’s most ardent foes. As Hezbollah reeled, Israel struck again, pounding the group’s headquarters, arsenals and logistic centers with 2,000-pound bombs.

The largest series of airstrikes occurred on Sept. 27, 10 days after the pagers exploded. The attack, targeting a deeply buried command center in Beirut, was ordered by Netanyahu as he traveled to New York for a United Nations speech in which he declared, speaking to Hezbollah, “Enough is enough.”

“We will not accept a terror army perched on our northern border, able to perpetrate another Oct. 7-style massacre,” Netanyahu said in the speech.

The next day, Sept. 28, Hezbollah confirmed what most of the world already knew: Nasrallah, the group’s fiery leader and sworn enemy of Israel, was dead.

Mekhennet reported from Tel Aviv, Jerusalem, Dubai and Amman, Jordan. Warrick reported from Washington and Amman.

previous coverage

• Pager attack on Hezbollah forces Iran-backed allies to rethink devices