Thousands of people were injured in Lebanon after pagers used by the militant group Hezbollah to communicate exploded across the country almost simultaneously on Tuesday.
At least nine people were killed in the blasts, and hundreds more were taken to hospitals across the country. The Lebanese Ministry of Health reports that at least 2,750 people have been injured, 200 of them seriously.
It is not clear how the attack was carried out, which appears to have been extremely sophisticated, although Hezbollah has blamed its adversary, Israel. Israeli officials have so far declined to comment.
Here's what's known so far.
The blasts began in southern Beirut and several other areas of Lebanon on Tuesday afternoon around 3:45 p.m. local time.
Witnesses reported seeing smoke coming out of people's pockets before seeing small explosions that sounded like fireworks and gunshots.
One of the video surveillance clips shows an explosion in the pants pocket of a man who is standing at the cash register of a store.
The explosions continued for about an hour after the first blasts, the BBC reported.
Soon after, dozens of people began arriving at hospitals in Lebanon, and witnesses described mass confusion.
A source close to Hezbollah told AFP that two of those killed were the sons of two Hezbollah lawmakers. He also claimed that the daughter of a Hezbollah member had been killed.
Iran's ambassador to Lebanon, Mohtaba Amani, is among the wounded. According to Iranian meia reports, his injuries were minor.
Hezbollah leader Hassan Nasrallah was not injured in the explosions.
According to the UK-based Syrian Observatory for Human Rights, 14 people were injured in similar blasts in neighboring Syria.
Analysts were quick to express their shock at the scale of the attack, saying Hezbollah prides itself on its security measures.
Some have suggested that the hacking attack may have caused the pagers' batteries to overheat, causing the devices to explode. Such an act would be unprecedented.
But many experts say that's unlikely, as footage of the explosions doesn't match the batteries overheating.
Some analysts say it's more likely a supply chain attack where the pagers were tampered with during production or in transit.
Supply chain attacks are an increasingly serious problem in the cybersecurity world, with many of the high-profile incidents recently being caused by hackers gaining access to products while they are in development.
But these attacks are usually limited to software. Hardware supply chain attacks are much less common because they involve access to the device.
If this was indeed a supply chain attack, it would have involved a massive operation to covertly tamper with the pagers in some way.
A former British Army munitions expert, who asked not to be named, told the BBC that the devices may have been filled with 10-20 grams of a military-grade explosive hidden in a fake electronic component.
According to the expert, this device was triggered by a signal called an alphanumeric text message.
So far, no one has claimed responsibility, although Lebanon's prime minister and Hezbollah have blamed Israel.
Prime Minister Najib Mikati said the explosions constituted "a serious violation of Lebanon's sovereignty and a crime by all standards."
In a statement accusing Israel of being behind the attacks, Hezbollah said it held the country "fully responsible for this criminal aggression, which also targets civilians."
"This insidious and criminal enemy will surely receive his just punishment for this sinful aggression, whether he expects it or not," she added.
Israeli officials have not commented on the allegations, but most analysts agree that it seems likely that she was behind the attack.
Professor Simon Mabon, head of international affairs at Lancaster University, told the BBC: "We know Israel has a precedent for using technology to track its targets" - but he called the scale of this attack "unprecedented".
Lina Khatib of UK-based Chatham House said the attack suggested Israel had penetrated "deeply" into Hezbollah's "communications network".
Hezbollah relies heavily on pagers for the group's communications.
Cell phones have long been dismissed as too vulnerable, as demonstrated by the 1996 killing of Israeli Hamas bomber Yahya Ayash when his phone exploded in his hand.
But one Hezbollah operative told the AP news agency that the pagers were a new brand that the group had not used before.
Emily Harding, a former CIA analyst, said the security breach was deeply embarrassing for Hezbolla
"A breach of this magnitude is not only physically damaging, but it will make them question their entire security apparatus," she told the BBC.
"I expect them to conduct an intensive internal investigation that will distract them from the potential battle with Israel."
Hezbollah is an ally of Israel's sworn enemy in the region - Iran. The group is part of Tehran's "Axis of Resistance" and has been waging a low-level war with Israel for months, frequently exchanging rockets and projectiles along Israel's northern border. Entire communities have been displaced on both sides.
The blasts came just hours after Israel's security cabinet announced the safe return of residents in the country's north to an official military target.
Prime Minister Benjamin Netanyahu told a visiting US official that Israel "will do what is necessary to ensure its security".
Earlier on Monday, Israel's Internal Security Agency said it had foiled an attempt by Hezbollah to kill a former employee.
Despite ongoing tensions, observers say the two sides have so far sought to limit hostilities without crossing the line into full-scale war. However, there are fears that the situation could spiral out of control, as Hezbollah has already threatened to respond to the September 17 blasts. | BGNES
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