At least 14 people were killed, and 450 others were injured after communications devices used by Hezbollah detonated in Lebanon's south and southern suburbs of the capital Beirut in the second wave of attacks thought to be carried out by Israel late Wednesday.
At least one of the blasts took place near a funeral organized by Hezbollah for those killed the previous day when thousands of pagers used by the group exploded across the country.
A source close to Hezbollah said walkie-talkies used by its members blew up in its Beirut stronghold, with state media reporting similar blasts in south and east Lebanon.
AFPTV footage showed people running for cover when an explosion went off during a funeral for Hezbollah militants in south Beirut on Wednesday afternoon.
Lebanese Foreign Minister Abdallah Bou Habib warned the "blatant assault on Lebanon's sovereignty and security" was a dangerous development that could "signal a wider war."
The influx of so many casualties all at once overwhelmed hospitals in Hezbollah strongholds.
At a Beirut hospital, doctor Joelle Khadra said "the injuries were mainly to the eyes and hands, with finger amputations, shrapnel in the eyes – some people lost their sight."
A doctor at another Beirut hospital, requesting anonymity because he was not authorized to speak to the media, said he had worked through the night and that the injuries were "out of this world – never seen anything like it."
The group said on Wednesday it had attacked Israeli artillery positions with rockets in the first strike at its arch-foe since pager blasts wounded thousands of its members in Lebanon and raised the prospect of a wider Middle East war.
Israel's spy agency Mossad, which has a long history of covert operations on foreign soil, planted explosives inside pagers imported by Hezbollah months before Tuesday's detonations, a senior Lebanese security source and another source told Reuters.
The death toll rose to 12, including two children, Lebanese Health Minister Firass Abiad said on Wednesday. Tuesday's attack wounded nearly 3,000 people, including many of the Lebanese group's fighters and Iran's envoy to Beirut.
A Taiwanese pager maker denied that it had produced the pager devices which exploded in an audacious attack that raised the prospect of a full-scale war between the Iran-backed Hezbollah and Israel.
Gold Apollo said the devices were made by under licence by a company called BAC, based in Hungary's capital Budapest.
There was no immediate word on when Hezbollah had launched its latest rocket attack, but normally the group announces such strikes shortly after carrying them out, suggesting it fired at the Israeli artillery positions on Wednesday.
Hezbollah has vowed to retaliate against Israel, whose military declined to comment on the blasts. The two sides have been engaged in cross-border warfare since the Gaza conflict erupted last October, fuelling fears of a wider Middle East conflict that could drag in the United States and Iran. Jordan's Foreign Minister Ayman Safadi accused Israel of pushing the Middle East to the brink of a regional war by orchestrating a dangerous escalation on many fronts.
"Hezbollah wants to avoid an all-out war. It still wants to avoid one. But given the scale, the impact on families, on civilians, there will be pressure for a stronger response," said Mohanad Hage Ali of the Carnegie Middle East Center.
One Hezbollah official said the detonation was the group's "biggest security breach" in its history.
Footage from hospitals reviewed by Reuters showed men with various injuries, some to the face, some with missing fingers and gaping wounds at the hip where the pagers were likely worn.
The plot appears to have been many months in the making, several sources told Reuters. It followed a series of assassinations of Hezbollah and Hamas commanders and leaders blamed on Israel since the start of the Gaza war.