The New York Times reported that Israel carried out its operation against Hezbollah on Tuesday by hiding explosive materials inside a new batch of Taiwanese-made communication devices that were imported into Lebanon, according to American and other officials familiar with the operation.

The communications devices ordered by Hezbollah from Taiwanese company Gold Apollo were tampered with before they arrived in Lebanon, according to some officials. Most were the company’s AP924 model, though three other Gold Apollo models were included in the shipment.

The explosive, weighing no more than one to two ounces, was planted next to the battery in each communication device, two officials said. A switch was also included that could be activated remotely to detonate the explosives.

At 3:30 p.m. in Lebanon, the radios received a message that appeared to come from Hezbollah leadership, according to officials. Instead, the message activated the explosives. Lebanon’s health minister told state media that at least 11 people were killed and more than 2,700 wounded.

The devices were programmed to beep for several seconds before exploding, according to three officials.

Hezbollah accused Israel of orchestrating the attack but gave limited details of its understanding of the operation. Israel has not commented on the attack, nor said it was behind it.

The U.S. and other officials spoke on condition of anonymity because of the sensitive nature of the operation.

Independent cybersecurity experts who studied footage of the attacks said the force and speed of the explosions were clearly caused by some type of explosive material.

“These devices were likely modified in some way to cause these types of explosions – the size and power of the explosion suggests it wasn’t just the battery,” Mikko Hypponen, a research specialist at software company WithSecure and a cybercrime advisor to Europol, told the newspaper.

The attacks targeted Hezbollah where they were most vulnerable, said Keren Elazari, a cybersecurity analyst and Israeli researcher at Tel Aviv University.

Earlier this year, Hezbollah leader Hassan Nasrallah imposed strict restrictions on the use of cell phones, which he saw as more vulnerable to Israeli surveillance, according to some officials and security experts.

“This attack hit them at their weak point because they removed a central means of communication,” Al-Azari said. “We have seen these types of devices, pagers, targeted before but never in an attack of this complexity.”

More than 3,000 pagers were ordered from Taiwanese company Gold Apollo, several officials said. Hezbollah distributed the pagers to its members across Lebanon, and some reached Hezbollah allies in Iran and Syria. Israel’s attack affected the pagers that were activated and receiving messages.

US State Department spokesman Matthew Miller said on Tuesday, in response to a question from the Jerusalem correspondent at his daily press conference at the US State Department, that the United States had no involvement or knowledge of these explosions, noting that experts believe that this type of technology, which relies on artificial intelligence only, is available to the US military, which uses it from the air via C-130 aircraft.

The attack, which Hezbollah attributed to Israel in a statement, directly contradicts the Biden administration’s ongoing, intensive efforts to maintain diplomatic efforts rather than military escalation. Hours earlier, US envoy Amos Hochstein had urged senior Israeli officials not to escalate the conflict with Hezbollah, warning of potentially dire consequences.

Hochstein made direct appeals to both Prime Minister Benjamin Netanyahu and Defense Minister Yoav Galant—whom U.S. officials have long considered their preferred interlocutor in the Israeli security cabinet—to advocate for a diplomatic solution on the Israeli-Lebanese border. Galant’s hawkish views on Lebanon have been a source of concern among U.S. officials since the aftermath of Oct. 7. Galant’s potential dismissal is a source of concern for U.S. officials—both for the defense minister’s dismissal on the cusp of a regional war and for the unceremonious dismissal of a balanced voice in Israel’s hardline cabinet.

It was not clear on Tuesday exactly when the pagers were ordered and when they arrived in Lebanon.