Pagers belonging to Hezbollah members across Lebanon and in some parts of Syria exploded in what appeared to be a coordinated incident on Tuesday. At least 200 people were considered to be seriously injured by the explosions.
Here's what we know so far.
Who made the pagers?
Following a report by The New York Times that the pagers were made by Taiwanese company Gold Apollo, the company issued a statement saying the devices were manufactured in Hungary.
"The product was not ours. It was only that it had our brand on it," the Gold Apollo founder and president, Hsu Ching-kuang, told reporters at the company's offices in the northern Taiwanese city of New Taipei on Wednesday.
Gold Apollo said it has a licensing agreement with Hungarian firm BAC Consulting KFT. The pagers in question were "produced and sold by BAC," Gold Apollo said in a statement.
BAC has not commented on the reports.
How did the pagers explode?
Hsu said he did not know how the pagers could have exploded.
At around 3:45 local time in Beirut, the devices began exploding and continued doing so for about an hour. Witnesses reported hearing sounds like a firework going off and seeing smoke explode from people's pockets.
Experts believe that the explosives were put in place sometime before delivery in what would have been a sophisticated supply chain infiltration.
Reuters news agency reported that a senior Lebanese security official believes this was carried out by Israel's Mossad spy agency.
Device attacks typically involve remote software hacks. Tampering with hardware on this scale is extremely rare.
How has Hezbollah replied?
Hezbollah promised on Wednesday to punish Israel for its "criminal aggression" one day after nine people, including a child, were killed and 2,800 were wounded in an attack on the group."We hold the Israeli enemy fully responsible for this criminal aggression," the group said in a statement, adding that Israel "will certainly receive its just punishment for this sinful aggression."
In a separate statement, the group said that it "will continue" the fight for Gaza.
Hezbollah chief Hassan Nasrallah is set to make a speech on the "latest developments" on Thursday.
How has Israel replied?
Israel has not yet commented on the attack. The explosions came hours after the Israeli government said it was widening the goals of its nearly year-long war with Hamas in Gaza to include thesafe return of Israeli citizens to their homes in the north of the country near the border to Lebanon.
Near daily conflict between Israeli forces and Hezbollah near the Israel-Lebanon border has killed dozens of fighters and forced thousands on both sides of the border to flee their homes in recent months.
Why do Hezbollah members use pagers?
Pagers were one of the first widely used wireless means of communication. They can carry simple alphanumeric or voice messages.
Militants have turned to this relatively low-tech tool to evade surveillance.
Nasrallah has previously warned members to carry mobile phones, which can be tracked and hacked. A member of Hezbollah told the Associated Press that the Gold Apollo AR-924 pagers were new and not a model they had used before.