An Israeli air strike targeted a senior Hezbollah commander in Beirut's southern suburbs late on Tuesday.
The Israeli military said it was in retaliation for a cross-border rocket attack three days before that killed 12 children and teenagers.
A loud blast was heard and a plume of smoke could be seen rising above the southern suburbs - a stronghold of the armed group Hezbollah - at around 7:40 pm (1640 GMT), a Reuters witness said.
A senior Lebanese security source said a senior Hezbollah commander had been the target of the air strike and his fate remained unclear.
Lebanon's state-run national news agency said an Israeli air strike had targeted the area around Hezbollah's Shura Council in the Haret Hreik neighbourhood of the capital.
Beirut has been on edge for days ahead of an anticipated Israeli attack in reprisal for the rocket strike on the Israeli-occupied Golan Heights on Saturday that killed the 12 youngsters in a football field in a Druze village.
Hezbollah has denied involvement in that attack.
As diplomats sought to contain the fallout, US Defence Secretary Lloyd Austin said he did not believe a fight was inevitable between Hezbollah and Israel, though he remained concerned about the potential for escalation.
Gaps in Gaza ceasefire talks under way in Qatar between Israel and Hamas can be bridged but it may take more than a few days to reach a deal, Israeli officials said on Tuesday.
US President Donald Trump held talks with Israeli Prime Minister Benjamin Netanyahu at the White House on Monday, while Israeli officials continued indirect negotiations with Hamas aimed at securing a Gaza ceasefire and hostage-release deal.
Search teams plodded through muddy riverbanks and flew aircraft over flood-ravaged central Texas as hopes dimmed of finding survivors from a disaster that has claimed at least 96 lives, many of them children.
Four workers were killed and at least 22 others were injured in a fire that broke out on Monday at a key data centre in Cairo, Hossam Abdel Ghaffar, the spokesperson at Egypt's Health Ministry, told Reuters on Tuesday.
President Donald Trump said on Monday the US would send more weapons to Ukraine, primarily defensive ones, to help the war-torn country defend itself against intensifying Russian advances.