Lebanon's health ministry said 20 people were killed and more than 450 injured on Wednesday in the second wave of communication device explosions.
The blasts came a day after the simultaneous detonation of pagers used by Hezbollah killed 12 people, including two children, and wounded up to 2,800 others across Lebanon, in an unprecedented attack blamed on Israel.
Walkie-talkies used by its members exploded in the latest blasts at Hezbollah's Beirut stronghold, a source close to the group said, with state media reporting similar detonations in south and east Lebanon.
There was no comment from Israel, which only hours before Tuesday's explosions had announced it was broadening the aims of its war in Gaza to include its fight against Hamas's ally Hezbollah.
"The centre of gravity is moving northward," Israeli Defence Minister Yoav Gallant said during a visit to an air base on Wednesday. "We are at the start of a new phase in the war."
Amos Harel of the left-leaning Haaretz newspaper said the pager and walkie-talkie blasts had put "Israel and Hezbollah on the brink of all-out war".
With tensions spiralling, senior diplomats from the United States, Britain, Germany, France and Italy will meet on Thursday in Paris, sources said, ahead of a UN Security Council meeting planned for Friday.
US Secretary of State Antony Blinken will join his counterparts in the French capital after discussing the possibility of a Gaza war truce in Cairo.
The White House warned all sides against "an escalation of any kind", while UN Secretary-General António Guterres called for an end to the upsurge in violence in the Middle East.
Guterres was deeply alarmed by reports that a large number of devices exploded in Lebanon and Syria over the past two days, his Spokesperson said in a statement “The Secretary-General urges all concerned actors to exercise maximum restraint."

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