Hezbollah was delivering the new Gold Apollo bombers to its members hours before they started exploding or even after the thousands of explosions began, two security sources told Reuters, indicating the Shiite group was confident the devices were safe.

A member of the organization received the new buzzer on Monday and it exploded the next day while still in its box, one of the sources said.

Another buzzer given to a senior official a few days earlier injured a junior official when it went off, a second source said.

In a coordinated attack, Gold Apollo bombers exploded on Tuesday in Hezbollah strongholds in southern Lebanon, the suburbs of Beirut and the eastern Bekaa Valley.

On Wednesday, it was the turn of hundreds of Hezbollah radios to explode.

The attacks killed 37 people, including at least two children, and injured more than 3,000 people.

The batteries of the radios were laced with the highly explosive PETN, another Lebanese source told Reuters on Friday.

Up to three grams of explosives hidden in the bombers went undetected for months by Hezbollah, Reuters reported earlier this week.

One of the security sources said it was very difficult to detect the explosives “with any device or scanner”.

The source did not specify what kind of scanners Hezbollah had put the bombers through.

Hezbollah tested the devices after they were delivered to Lebanon starting in 2022, and also passed them through airports to ensure they did not set off alarms, two additional sources told Reuters.

In total, Reuters spoke to 6 sources familiar with the details of the explosive devices for this story.

The sources did not specify the name of the airports where the tests were carried out.

Lebanon and Hezbollah say Israel was behind the attacks. Israel’s secret military intelligence unit 8200 was involved in the planning, a Western security source told Reuters this week. Israel, which has since stepped up airstrikes in Lebanon, has neither denied nor confirmed its involvement.

The attacks and the distribution of the devices despite routine scanning and checks for breaches have damaged Hezbollah’s reputation as the most formidable umbrella of Iran-allied “Axis of Resistance” of anti-Israeli irregular forces across the Middle East.

In a televised address on Thursday, Hezbollah leader Hassan Nasrallah said the attacks were “unprecedented in the history” of the group.

Taiwan-based Gold Apollo said it did not manufacture the devices used in the attack, saying they were made by a company in Europe licensed to use the company’s brand. Reuters was unable to determine where they were manufactured or at what point they were tampered with.

A batch of 5,000 buzzers was imported into Lebanon earlier this year. Reuters previously reported that Hezbollah turned to the bombers in an attempt to avoid Israeli surveillance of its cellphones, after killing senior commanders in targeted airstrikes last year.

Hezbollah’s conflict with Israel dates back decades, but has flared up in the past year alongside the Gaza war, heightening fears of an all-out regional war.