The sophisticated attacks on communications equipment used by Iran-backed armed group Hezbollah have sown disarray in Lebanon, and are increasingly viewed as heralding a return to all-out war, last fought 18 years ago.

Hand-held radios used by Hezbollah detonated on Wednesday across Lebanon's south in the country's deadliest day since cross-border fighting erupted between the militants and Israel in parallel with the Gaza war nearly a year ago.

The previous day, hundreds of pagers - used by Hezbollah to evade mobile phone surveillance - exploded at once, killing 12 people including two children, and injuring nearly 3,000.

Israel has not commented directly on the attacks, but multiple security sources have said was carried out by its spy agency Mossad.

Israeli security services said on Thursday they had arrested an Israeli citizen last month on suspicion of involvement in an Iranian-backed assassination plot. The businessman with connections in Turkey had attended at least two meetings in Iran to discuss assassinating Prime Minister Benjamin Netanyahu, the defence minister or the head of the Shin Bet spy agency.

Overnight, Israeli jets and artillery hit multiple targets in southern Lebanon, Israel's military said.

The military said air strikes hit Hezbollah targets in Chihine, Tayibe, Blida, Meiss El Jabal, Aitaroun and Kfarkela in southern Lebanon, as well as a Hezbollah weapons storage facility in the area of Khiam.

Israeli media reported that a number of Israeli civilians had been wounded by anti-tank missile fire from Lebanon but there was no official confirmation.

On Wednesday, Hezbollah fired around 20 projectiles into Israel, most of which were intercepted by air defence systems without causing any injuries, the military said.

SHIFTING FOCUS

Israel and Hezbollah have been exchanging fire across the Israeli-Lebanon border in parallel with the war Israel has waged in Gaza against Hamas, the Palestinian militant group whose fighters attacked Israel on Oct. 7.

Tens of thousands of people have had to flee the Israel-Lebanon border area on both sides. Netanyahu vowed on Wednesday to return the evacuated Israelis "securely to their homes".

On Wednesday, Israeli Defence Minister Yoav Gallant said the war was moving into a new phase, with more resources and military units now being shifted to the northern border.

According to Israeli officials, the forces being deployed there include the 98th Division, an elite formation including commando and paratroop elements that has been fighting in Gaza.

Hezbollah launched missile barrages on Israel on the day after the Oct. 7 attack by Hamas and since then there has been a constant exchange of fire that neither side has allowed to escalate into a full-scale war.

However, tens of thousands have been evacuated on both sides of the border, and there has been mounting pressure in Israel for the government to get the evacuees back home.