Hezbollah said it launched Katyusha rockets at a north Israel intelligence base it blamed for targeted killings, claiming its first attack after Israel launched a deadly strike on the group's south Beirut stronghold, a day after the group's leader Sayyed Hassan Nasrallah vowed to retaliate against Israel for the device blasts carnage.

The Iran-backed group said its fighters had targeted "the main intelligence headquarters in the northern region responsible for assassinations... with volleys of Katyusha rockets", adding the attack was "in response to the Israeli enemy's attacks" on south Lebanon.

An initial investigation by Lebanese authorities has found that hand-held devices that exploded this week were booby-trapped before they entered the country, Lebanon's mission to the United Nations said.

The head of the World Health Organization says it is working with Lebanon’s Health Ministry as it deals with those wounded by exploding communications devices.

WHO Director-General Tedros Adhanon Ghebreyesus said the strikes have “severely disrupted Lebanon’s already-fragile health system.”

The UK’s top diplomat is urging British nationals to leave Lebanon.

Foreign Secretary David Lammy said the situation could deteriorate rapidly after consecutive rounds of explosive attacks that hit devices carried by Hezbollah members, killing 37 people and wounding around 3,000 others.

Israel is accusing Iran and Hezbollah of bombarding millions of Israelis with threatening text messages as the conflict between the Israeli military and the Lebanese militant group escalated.

Israel's National Cyber Directorate said Thursday that a flood of Hebrew-language text messages popped up on cellphones nationwide, falsely purporting to be a communication from the Israeli Home Front Command.

Israeli Defense Minister Yoav Gallant has said Hezbollah would “pay an increasing price” as Israel claims to be seeking to make conditions near its border with Lebanon safe enough for residents to return.

"Hezbollah is feeling chased and the sequence of our military operations will continue," Gallant added, in a possible hint that Israel was behind the deadly pager and walkie-talkie blasts that rocked Lebanon on Tuesday and Wednesday leaving 37 people dead and around 3,000 injured, many of them severely.

Two people from Taiwanese companies were questioned as part of a probe into pagers that exploded while being used by Hezbollah operatives in Lebanon, investigators said Friday, as top officials insisted the devices were not from the island.

Questions and speculation have swirled over where the devices came from and how they were supplied to the Lebanese group after hundreds of pagers and walkie-talkies detonated across Lebanon on Tuesday and Wednesday, killing at least 37 people and wounding nearly 3,000.

Israel's military said overnight that its jets hit around 100 Hezbollah targets in south Lebanon in two waves of intense airstrikes.

"Approximately 100 launchers and additional terrorist infrastructure sites, consisting of approximately 1,000 barrels" set to be fired immediately were hit, the Israeli army said.

Bulgarian authorities said on Friday a company based in Sofia had nothing to do with the delivery of exploding communications devices to Hezbollah.

Hundreds of pagers and walkie-talkies detonated across Lebanon on Tuesday and Wednesday, killing at least 37 people, wounding nearly 3,000 and generating panic.

Israel's army announced new strikes on Hezbollah targets in Lebanon on Thursday, as warning sirens rang out in northern Israel, indicating possible incoming fire.