At least eight people were killed and 2,800 more members of Hezbollah were reportedly injured when the pagers they use to communicate simultaneously exploded on Tuesday.
Lebanon's state-run news agency said the blasts targeted people across Beiruit. Others were injured in Syria.
A Hezbollah official told the National News Agency that it was the "biggest security breach yet" targeting the Iran-backed group, according to Reuters.
One of the blasts was caught on camera at a market.
Iranian Ambassador Lebanon Mojtaba Amani is among the injured, the Times of Israel reported.
Israel has been battling Hezbollah for months. It did not immediately take credit for the attacks.
But earlier in the day it said that halting Hezbollah's attacks in the country's north is now an official war goal.
Israeli officials have threatened to take heavier military action against the armed group.
While the focus of the war has been on Gaza, the unabating exchanges of fire between Israeli troops and Hamas ally Hezbollah in Lebanon have forced tens of thousands of people on both sides of the border to flee their homes.
"The political-security cabinet updated the goals of the war this evening, so that they include the following section: the safe return of the residents of the north to their homes," Israeli Prime Minister Benjamin Netanyahu's office said in a statement.
Not formally declared as a war, the exchanges of fire between Israeli troops and Hezbollah have killed hundreds of mostly fighters in Lebanon, and dozens of civilians and soldiers on the Israeli side, the AFP reported.
