The Israeli military said it has carried out a “precise strike” on the central headquarters of Hezbollah in Beirut.
Army spokesman Daniel Hagari made the announcement in a televised address after the explosion in Beirut sent massive clouds of orange and black smoke billowing in the skies.
Ambulances were seen heading to the scene of the explosions, sirens wailing.
Three major Israeli TV channels said Hezbollah leader Hassan Nasrallah was the target of the strikes. But the unsourced reports could not immediately be confirmed by The Associated Press, and the army declined comment.
But given the size and timing of the blast, there were strong indications that a high-value target may have been inside the buildings struck.
The strike came an hour after thousands of people attended the funeral of a top Hezbollah commander who was killed the day before.
Earlier in the day, an Israeli airstrike killed a family of nine in a Lebanese border village, authorities said, as Lebanon struggled to deal with a rising death toll, a wave of tens of thousands fleeing their homes and the possibility of an all-out war between Israel and Hezbollah.
As the two sides continued to trade fire, Israeli Prime Minister Benjamin Netanyahu addressed world leaders at the UN, vowing “continue degrading Hezbollah” until Israel achieves its goals along the Lebanon border, further dimming hopes for an internationally backed ceasefire.
Israel dramatically intensified its airstrikes in Lebanon this week, saying it is determined to put an end to more than 11 months of Hezbollah fire into its territory.
The scope of Israel’s operation remains unclear, but officials have said a ground invasion to push the militant group away from the border is a possibility.
Israel has moved thousands of troops toward the border in preparation.
That has Lebanese fearing a repeat of the last Israel-Hezbollah war, in 2006, which lasted a month and wreaked heavy destruction over parts of their country.
Or worse, they fear, Lebanon could suffer devastation on the scale wreaked in Gaza by Israel’s nearly year-long campaign against Hamas.
At least 25 people were killed in Israeli strikes early on Friday, health minister Firass Abiad said, bringing the death toll in Lebanon this week to more than 720. He said the dead included dozens of women and children.
The Israeli military said it carried out dozens of strikes over the course of two hours around the south on Friday, including in the cities of Sidon and Nabatiyeh.
It said it was targeting Hezbollah rocket launchers and infrastructure. It said Hezbollah fired a volley of rockets toward the northern Israeli city of Tiberias.
