NEW YORK (AP) — Just a day after pagers used by hundreds of members of the militant group Hezbollah exploded, more electronic devices detonated in Lebanon on Wednesday in what appears to be a second wave of sophisticated, deadly attacks targeting an extraordinary number of people.

Both attacks, which many believe were carried out by Israel, have heightened fears that the simmering conflict between the two sides could escalate into open war. This week’s explosions have also heightened concerns about the range of potentially vulnerable explosive devices, especially after so many civilians have been killed or injured in such bombings.

Here’s what we know so far:

What happened during these two waves of attacks?

On Tuesday, the pagers of hundreds of Hezbollah members exploded almost simultaneously in parts of Lebanon and Syria. The attack killed at least 12 people – including two small children – and injured thousands.

A U.S. official, speaking on condition of anonymity, said Israel had informed the United States of the operation, which detonated small amounts of explosives hidden in the pagers. The Lebanese government and Iran-backed Hezbollah also blamed Israel for the deadly explosions. The Israeli military, which has a long history of sophisticated operations behind enemy lines, declined to comment.

A day after those deadly explosions, more detonations occurred in Beirut and parts of Lebanon on Wednesday. Several explosions were heard at a funeral in Beirut, where three Hezbollah members and a child were killed in Tuesday’s blasts, Associated Press journalists at the scene reported.

At least 20 people were killed and another 450 injured in what appears to be the second attack, the Health Ministry said.

In his speech to troops on Wednesday, Israeli Defense Minister Yoav Gallant made no mention of the explosions of electronic devices, but praised the work of the Israeli army and security agencies and said: “We are at the beginning of a new phase of the war.”

What types of equipment were used?

A Hezbollah official told AP that the group’s walkie-talkies exploded on Wednesday. The official spoke on condition of anonymity because he was not authorized to speak to the media. Lebanon’s official news agency also reported that solar panels in houses exploded in several areas of Beirut and southern Lebanon, injuring at least one girl.

While the details of Wednesday’s attack are not yet fully clear, the second wave of explosions targeted a country still reeling from Tuesday’s pager bombings. That attack appears to have been a complex Israeli operation against Hezbollah, but numerous civilian casualties were also reported as the detonations occurred wherever Hezbollah members’ pagers were located – including homes, cars, grocery stores and cafes.

Hezbollah has been using pagers as a means of communication for years, and recently Hezbollah leader Hassan Nasrallah warned members of the group against carrying cell phones because Israel could use them to track the group’s movements.

Pagers also run on a different wireless network than cell phones, which typically makes them more resilient in emergencies. And for a group like Hezbollah, the pagers were a way to circumvent what is believed to be Israel’s intensive electronic surveillance of cell phone networks in Lebanon – because pager technology is simpler and carries less risk of calls being intercepted.

Elijah J. Magnier, a Brussels-based veteran and senior political risk analyst who said he has spoken to Hezbollah members and survivors of the attack, said the newer pagers used in Tuesday’s explosions were acquired more than six months ago. How they got to Lebanon is still unclear.

Taiwanese company Gold Apollo said Wednesday that it had authorized the use of its trademark on the AR-924 pager model, but said the pagers were manufactured and sold by a Budapest, Hungary-based company called BAC Consulting KFT.

Taiwan’s Ministry of Economic Affairs said there were no records of direct exports of Gold Apollo pagers to Lebanon. And a Hungarian government spokesman later added that the pagers had never been in Hungary either, as BAC had only acted as an intermediary.

There is also speculation about the origin of the devices that exploded on Wednesday. A sales manager at the US subsidiary of the Japanese walkie-talkie manufacturer Icom told the Associated Press that the radios that exploded in Lebanon were apparently counterfeits and were not manufactured by Icom.

“I can guarantee you it was not our products,” Ray Novak, senior sales manager for Icom’s amateur radio division, said Wednesday in an interview at a trade show in Providence, Rhode Island.

Novak said Icom introduced the V-82 model more than two decades ago and it has long been out of service. It was designed for amateur radio operators and for use in social or emergency communications, including tracking tornadoes or hurricanes, he said.

What kind of sabotage would cause these devices to explode?

Tuesday’s explosions were most likely the result of supply chain disruptions, several experts told the Associated Press, pointing out that very small explosive devices may have been built into the pagers before they were delivered to Hezbollah and then detonated all at once remotely, possibly with a radio signal, confirming the U.S. official’s account.

A former British Army bomb disposal officer explained that an explosive device consists of five main components: a container, a battery, a trigger device, a detonator and an explosive charge.

“A pager already has three of them,” said the former police officer, who asked to remain anonymous because he now works as a consultant for clients in the Middle East. “You just need to add the detonator and the charge.”

This suggests the involvement of a state actor, said Sean Moorhouse, a former British army officer and explosive ordnance disposal expert. He added that the Israeli foreign intelligence agency Mossad was the most obvious suspect with the means to carry out such an attack. Israel has a long history of Carrying out similar operations in the past.

The exact details of Wednesday’s explosions are still unclear, but reports of further explosions of electronic devices suggest that even more booby traps are being used in the Lebanese supply chain. This also heightens concerns about the lack of certainty about who might have the tampered devices.

How long did this operation take?

Planning an attack of this magnitude would take a long time. The exact details are still unknown, but experts who spoke to AP about Tuesday’s explosions said the time span was between a few months and two years.

The sophistication of the attack suggests the perpetrator has been gathering information for a long time, said Nicholas Reese, a lecturer at the Center for Global Affairs at New York University’s School of Professional Studies. An attack of this caliber requires building the relationships needed to gain physical access to the pagers before they are sold, developing the technology that can be embedded in the devices and finding sources that can confirm that victims were carrying the pagers.

Citing conversations with Hezbollah contacts, Magnier said the group is currently investigating what type of explosives were used in the device. They suspect RDX or PETN, highly explosive materials that can cause significant damage with just 3 to 5 grams. They also wonder whether the device had a GPS system that would allow Israel to track the movements of group members.

NR Jenzen-Jones, a military weapons expert and director of Australia-based Armament Research Services, added that “such a large-scale operation also raises questions about targeting” – highlighting the number of casualties and the enormous impact reported so far.

“How can the person who detonates the explosive device be sure that, for example, the target person’s child will not play with the pager if it works?” he asked.

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Associated Press journalists Johnson Lai in Taipei, Bassem Mroue in Beirut and Matt O’Brien in Providence, Rhode Island, contributed to this report.