Hundreds of pagers exploded in Lebanon, Syria in deadly attack. Here’s what we know.

NEW YORK In a sophisticated remote attack, pagers used by hundreds of Hezbollah members exploded almost simultaneously in Lebanon and Syria on Tuesday, killing at least nine people — including an 8-year-old girl — and injuring thousands more.

The Iranian-backed militant group blamed Israel for the deadly explosions, which affected an unusually wide range of people and showed signs that it was a long-planned operation. How the attack was carried out is largely uncertain, and investigators did not immediately say how the pagers were detonated. The Israeli military declined to comment.

Here’s what we know so far.

Why were pagers used in the attack?

Hezbollah leader Hassan Nasrallah has previously warned the group’s members not to carry cellphones, saying they could be used by Israel to track the group’s movements. As a result, the organization uses pagers to communicate.

A Hezbollah official told The Associated Press that the exploding devices were from a new brand that the group had not used before. The official, who spoke anonymously because he was not authorized to speak to the press, did not name the brand or supplier.

Nicholas Reese, a lecturer at the Center for Global Affairs at New York University’s School of Professional Studies, explains that smartphones carry a greater risk of communications being intercepted compared to simpler technology such as pagers.

Such attacks will also force Hezbollah to change its communications strategy, said Reese, who previously worked as an intelligence officer, adding that survivors of Tuesday’s explosions would likely throw away “not just pagers, but phones, and leave behind tablets and other electronic devices.”

How could sabotage cause pagers to explode?

With little revealed by investigators so far, a range of theories emerged Tuesday about how the attack might have been carried out. Several experts who spoke to The Associated Press suggested the explosions were most likely the result of interference with the supply chain.

Very small explosive charges may have been incorporated into the pagers before being delivered to Hezbollah, and then all were detonated simultaneously, probably via a radio signal.

At the time of the attack, “the battery was probably half explosive and half regular battery,” said Carlos Perez, director of security intelligence at TrustedSec.

The former British Army sapper explained that an explosive device consists of five main parts: a container, a battery, a triggering device, a detonator and an explosive charge.

“The pager already has three of these,” said the former officer, who asked not to be identified because he now works as a consultant for Middle Eastern clients. “You just need to add a detonator and a charge.”

After surveillance footage emerged on social media on Tuesday showing a pager exploding on a man’s hip in a Lebanese market, two ammunition experts also said the explosion was most likely the result of a small explosive device.

“When you watch the footage, the force of the detonation is similar to that of an electrical detonator alone or one with an extremely small explosive charge,” said Sean Moorhouse, a former British Army officer and explosive ordnance disposal expert.

That’s a sign of state actor involvement, Moorhouse said. He added that the Israeli intelligence agency, Mossad, is the most obvious suspect with the resources to carry out such an attack.

NR Jenzen-Jones, a military weapons expert who is director of Australia’s Armament Research Services, agreed that the scale and sophistication of the attack “almost certainly point to a state actor” and that Israel has been accused of carrying out such operations in the past. Last year, the AP reported that Iran accused Israel of trying to sabotage its ballistic missile program with faulty foreign parts that could explode, damaging or destroying the weapons before they could be used.

How long did this operation take?

Planning an attack of this scale would take a long time. The exact details are still unclear, but experts who spoke to the AP offered estimates ranging from several months to two years.

The sophistication of the attack suggests that whoever was behind it had been gathering intelligence for a long time, Reese explained. An attack of this caliber requires building relationships to gain physical access to the pagers before selling them; developing the technology to be embedded in the devices; and finding sources who can confirm that the targets were carrying pagers.

And it’s likely that the infected pagers appeared normal to their users for some time before the attack. Elijah J. Magnier, a Brussels-based veteran and senior political risk analyst with more than 37 years of experience in the region, said he has spoken to Hezbollah members and survivors of Tuesday’s pager attack. He said the pagers were acquired more than six months ago.

“The pagers worked perfectly for six months,” Magnier said. The cause of the explosion, he said, was an error message sent to all the devices.

Magnier also said, based on conversations with Hezbollah members, that many of the pagers did not work, which allowed the group to examine them. They concluded that 3 to 5 grams of high-explosive material were hidden or embedded in the circuits, he said.

What else could have happened?

Another possibility is that malware may have been introduced into the pagers’ operating system — somehow causing all of the device’s batteries to overload at a certain time, causing them to catch fire.

According to a Hezbollah and Lebanese security official, the pagers first heated up and then exploded in the pockets or hands of the people carrying them on Tuesday afternoon.

The pagers operate on lithium-ion batteries, a Hezbollah official said. He said the devices exploded because they were targeted in an Israeli “security operation,” but did not provide further details.

If overheated, lithium-ion batteries can smoke, melt, or even catch fire. Lithium batteries are used in consumer products ranging from cell phones and laptops to electric cars. A lithium battery fire can reach temperatures of 590 C (1,100 F).

Still, Moorhouse and others noted that the photos and video footage seen Tuesday looked more like a small explosive device detonating than an overheating battery.

“A lithium-ion battery fire is one thing, but I’ve never seen one explode. It looks like a small explosive device,” said Alex Plitsas, a weapons expert at the Atlantic Council.

Among those raising the possibility of a supply chain attack is Jenzen-Jones, who adds that “an operation this large also raises questions about targeting” — highlighting the death toll and massive impact reported so far.

“How can the party initiating the explosive device be sure that, for example, the victim’s child is not playing with a pager while it is being activated?” he asked.