The “Israeli” spy agency planted explosives inside 5,000 pagers imported months before by Lebanese group Hezbollah, a senior Lebanese security source told Reuters.

The unprecedented operation was months in the making; the Lebanese group orders 5,000 pagers from Taiwanese company Gold Apollo, which were brought into the country earlier this year, believed to be somewhere around March/February – sometime after Hezbollah’s Secretary-General Hasan Nasrallah warned members of the group to stop using cellphones for security purposes.

The low-tech communication method was an attempt to evade “Israeli” intelligence and location-tracking.

"The Mossad injected a board inside of the device that has explosive material that receives a code. It's very hard to detect it through any means. Even with any device or scanner," another source told Reuters.

The pagers then exploded after a coded message was sent to the devices, the blast occurred 10 seconds after the initial beep so Hezbollah fighters could hold the device close to their face to read the message – per Hebrew media.

"This would easily be the biggest counterintelligence failure that Hezbollah has had in decades," said Jonathan Panikoff, the United States former deputy national intelligence officer on the Middle East.