The blasts that killed at least 37 people and wounded nearly 3,000 on Tuesday and Wednesday targeted communication devices used by the Iran-backed Hezbollah group.

Pagers and walkie-talkies exploded as their users were shopping in supermarkets, walking on streets and attending funerals, plunging the country into panic.

"International humanitarian law prohibits the use of booby-trap devices in the form of apparently harmless portable objects," the UN's High Commissioner for Human Rights, Volker Turk, told the Security Council during an emergency session on Lebanon requested by Algeria. 

"It is a war crime to commit violence intended to spread terror among civilians," he added, repeating his call for an "independent, rigorous and transparent" investigation.

Lebanese authorities blame Israel for the attack and have said the targeted devices were booby-trapped before they entered the country.

Hezbollah has vowed retribution and launched its own internal probe into the explosions. 

"I am appalled by the breadth and impact of the attacks," said Turk.

"These attacks represent a new development in warfare, where communication tools become weapons," he added. 

"This cannot be the new normal."

Speaking at the Security Council, Lebanon's top diplomat Abdallah Bou Habib called the attack "an unprecedented method of warfare in its brutality and terror."

"Israel, through this terrorist aggression has violated the basic principles of international humanitarian law," he said, calling Israel a "rogue state." 

Israel has not commented on the device blasts but has said it will widen the scope of its war in Gaza to include the Lebanon front.

"I can tell you that we will do everything we can to target those terrorists," Israel's ambassador to the UN Danny Danon told reporters on Friday when asked about the device explosions. 

He spoke after Israel announced it had killed the commander of Hezbollah's elite unit in a strike on Beirut on Friday.

"We have no intention to enter a war with Hezbollah in Lebanon, but we cannot continue the way it is," Danon said.

Speaking at the Security Council, Danon said Israel will do "whatever it takes" to restore security in northern areas. 

"If Hezbollah does not retreat from our border... through diplomatic efforts, Israel will be left with no choice but to use any means within our rights," he said.

Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, said the body was "very concerned about the heightened escalation" across the Lebanon-Israel frontier after Friday's Israeli strike on Beirut. 

He called for "maximum restraint" from all sides. 

Iran-backed Hezbollah is an ally of Palestinian militant group Hamas, which has been fighting a war in Gaza since its October 7 attack on Israel.

For nearly a year, the focus of Israel's firepower has been on Gaza but its troops have also been engaged in near-daily clashes with Hezbollah militants along its northern border.

Hundreds have been killed in Lebanon, most of them fighters, and dozens in Israel, including soldiers.