Pagers started exploding at around 3:30 pm local time, according to a statement from Hezbollah officials, who say that “various Hezbollah units and institutions” were impacted in the incident. The blasts continued for more than an hour, according A Hezbollah statement says a “large” number of people were injured and said they suffered from a wide variety of injuries.

In the immediate aftermath of the explosions, CCTV and phone footage posted to social media, which has not been independently verified, appears to show hospitals flooded with wounded people, as well as apparent explosions happening around waist height and images of damaged pagers. People with links to the region say the explosions caused street-level chaos.

“Hezbollah’s competent agencies are currently conducting a wide-ranging security and scientific investigation to determine the causes that led to these simultaneous explosions,” Hezbollah said in an initial statement.

Earlier Tuesday, Lebanon’s health minister, Firass Abiad, said 2,750 people had been wounded with 200 being critically injured. That number has since increased as the fallout from the attack becomes more clear. The country’s internal security unit made an for people to keep off the roads to allow people to be transferred to hospitals. Iran’s ambassador to Lebanon was injured in the blasts; separately, the Syrian Observatory for Human Rights said 14 people in the country had been injured by pager explosions

The perpetrator of the attack is widely believed to be Israel—fighting between Israel and Hezbollah, which is backed by Iran, has intensified since In a second statement issued after the explosions, reported by  Hezbollah blames Israel for the “criminal aggression that targeted civilians too.”

The Israel Defense Forces told WIRED it has “no comment.” Reuters reported that an unnamed “Hezbollah official” described the operation as the “biggest security breach” the group has faced in nearly a year of fighting with Israel.

It was not immediately clear how the attack was carried out. Initial reports on social media speculated that the pager explosions might have been triggered by digital hacking that caused the pagers’ batteries to overheat and explode.by the Lebanese Broadcast Corporation described preliminary reporting about a possible cyberattack. “According to information obtained by LBCI, initial reports suggest the pager server was compromised, leading to the installation of a script that caused an overload. This likely resulted in the overheating of the lithium battery, which then exploded.”

Footage posted on social media claiming to show examples of the explosions from around the country depict blasts that seemed too large to come from pager batteries alone. One photo  appeared to show a mangled pager with some legible make and model information that may point to the alphanumeric pager. Other reports indicate the pager model is the which has a lithium-ion battery.

The AP-900 runs on two AAA batteries, which,  could be induced to explode, but likely not with such force and scale as the explosions depicted in alleged videos of the blasts. If the pagers used by Hezbollah are the AR-924 or another model that runs on lithium-ion batteries, which can it’s still unlikely that a regular pager battery alone could produce blasts that could injure multiple people.

“Those explosions aren’t just batteries,” says Jake Williams, vice president of research and development at Hunter Strategy who formerly worked for the US National Security Agency. “Based on the reporting, these pagers were likely interdicted by Israeli authorities and modified with explosives. This highlights the risks of supply chain security, especially in places where technology is harder to ship to.”

Gold Apollo did not immediately respond to WIRED’s request for comment.

Williams points out that such an operation would likely involve operatives on both the tech distribution side and the Hezbollah procurement side. “You compromise the supply chain, but you don’t want thousands of explosive pagers running around Lebanon,” he says. “The mole gets them to exactly the right people.”

Some reports on Tuesday indicate that Hezbollah recently expanded its use of pagers in an attempt to secure communications after other channels had been infiltrated by Israeli intelligence. The Associated Press reported that an anonymous “Hezbollah official” said the group had recently adopted a “new brand” of pagers that “first heated up, then exploded.

“It’s unlikely that hacking was involved, as it’s likely that explosive material had to be inside the pagers to cause such an effect,” says Lukasz Olejnik, an independent consultant and visiting senior research fellow at King’s College London’s Department of War Studies. “Reports mention the delivery of new pagers recently, so perhaps the delivery was compromised.”

Michael Horowitz, head of intelligence at Middle East and North Africa risk management company Le Beck International, says if the attack is supply-chain-based, then it could have taken years to prepare and involved infiltrating a supplier and placing explosives inside new pagers.

“This is a major security breach, particularly if we’re talking about a charge that was placed inside the devices—which, in my opinion, is the most likely scenario,” Horowitz says. “This would mean that Israel has managed to infiltrate Hezbollah providers to the point of delivering hundreds (if not thousands) of devices used for secured communication.”

The incident comes amid escalations of fighting between Israel and Hezbollah in recent months, raising fears of a full-blown war. In the hours before the explosions on Tuesday, Israel said war goals would include allowing 60,000 people to return to Northern Israel after they were evacuated following Hezbollah attacks, and it would not rule out military action.

Horowitz says the incident could be a “prelude to a broader offensive” and possibly meant to disrupt Hezbollah’s communications networks. It is likely that replacing a large number of pagers would take some time to organize. Alternatively, Horowitz says, the attack could also have been conducted to show the “scale of Israel’s intelligence penetration.”

“This is a high-value operation that you wouldn’t use just to cause injuries,” Horowitz says.

Even if the blasts were not caused by a cyber-physical attack that induced the pager batteries to explode, it’s still possible that explosives planted in the pagers were detonated using a remote command, possibly even a specially crafted pager message.appeared to show users checking their pagers right as the explosions occurred, though this could have been coincidental.

The operation could have a psychological impact on Hezbollah given that bombs may have been lurking undetected in such an unassuming device. And though Tuesday’s attacks were notably aggressive, it would not be the first time Israeli intelligence has reportedly