Lebanon's Hezbollah was still handing its members new Gold Apollo branded pagers hours before thousands blew up this week, two security sources said, indicating the group was confident the devices were safe despite an ongoing sweep of electronic kit to identify threats.
One member of the Iranian-backed militia received a new pager on Monday that exploded the next day while it was still in its box, said one of the sources.
A pager given to a senior member just days earlier injured a subordinate when it detonated, the second source said.
In an apparently coordinated attack the Gold Apollo branded devices detonated on Tuesday across Hezbollah's strongholds of south Lebanon, Beirut's suburbs and the eastern Bekaa valley.
On Wednesday, hundreds of Hezbollah walkie-talkies exploded. The consecutive attacks killed 37 people, including at least two children, and injured more than 3,000 people.
The batteries of the walkie-talkies were laced with a highly explosive compound known as PETN, another Lebanese source familiar with the device's components told Reuters on Friday. Up to three grams of explosives hidden in the pagers had gone undetected for months by Hezbollah, Reuters reported earlier this week.
One of the security sources said it was very hard to detect the explosives "with any device or scanner." The source did not specify what type of scanners Hezbollah had run the pagers through.
Hezbollah examined the pagers after they were delivered to Lebanon, starting in 2022, including by traveling through airports with them to ensure they would not trigger alarms, two additional sources told Reuters. In total, Reuters spoke to six sources familiar with the details of the exploding devices for this story.
The sources did not specify the name of the airports where they conducted the tests.
Lebanon and Hezbollah say Israel was behind the attacks. Israel's secretive military intelligence Unit 8200 was involved in the planning, a Western security source told Reuters this week. Israel, which has since stepped up airstrikes on Lebanon, has neither denied or confirmed involvement.
Rather than a specific suspicion of the pagers, the checks had been part of a routine "sweep" of its equipment, including communications devices, to find any indications that they were laced with explosives or surveillance mechanisms, one of the security sources said.
The attacks, and the distribution of the devices despite the routine sweep and checks for breaches, have struck at Hezbollah's reputation as the most formidable of Iran's allied 'Axis of Resistance' umbrella of anti-Israel irregular forces across the Middle East.
In a televised speech on Thursday, Hezbollah Secretary-General Hassan Nasrallah said the attacks were "unprecedented in the history" of the group.
Hezbollah's media office and Israel's armed forces did not immediately respond to requests for comment for this story.
Taiwan-based Gold Apollo has said it did not manufacture the devices used in the attack, saying they were made by a company in Europe licensed to use the firm's brand. Reuters has not been able to establish where they were made or at what point they were tampered with.
A batch of 5,000 of the pagers were brought into Lebanon earlier this year. Reuters previously reported that Hezbollah turned to pagers in an attempt to evade Israeli surveillance of its mobile phones, following the killing of senior commanders in targeted airstrikes over the past year.
Hezbollah's conflict with Israel dates back decades but has flared up in the past year in parallel with the Gaza war, heightening worries of a full-blown regional war.
TOO LITTLE, TOO LATE
After the pagers detonated on Tuesday, Hezbollah suspected more of its devices may have been compromised, two of the security sources, as well as an intelligence source, told Reuters.
In response, it intensified the sweep of its communications systems, carrying out careful examinations of all devices. It also began investigating the supply chains through which the pagers were brought in, the two security sources said.
But the review had not been concluded by Wednesday afternoon, when the hand-held radios exploded.
Hezbollah believes that Israel opted to detonate the group's hand-held radios because it feared Hezbollah would soon find that the walkie-talkies were also rigged with explosives, one of the sources told Reuters.
The walkie-talkie explosions left 25 people dead and at least 650 injured, according to Lebanon's health ministry - a much higher fatality rate than the previous day's pager blasts, which killed 12 and wounded nearly 3,000.
That is because they carried a higher payload of explosives than the beepers, one of the security sources and the intelligence source said.
The group's probe into precisely where, when and how the devices were laced with explosives is ongoing, three of the sources said. Nasrallah later said the same in the speech on Thursday.
One of the security sources said Hezbollah had foiled previous Israeli operations targeting devices imported from abroad by the group - from its private landline telephones to ventilation units in the group's offices.
That includes suspected breaches in the past year.
"There are several electronic issues that we were able to discover - but not the pagers," the source said. "They tricked us, hats off to the enemy."