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.
Man charged with 10 counts of attempted murder after knife attack on UK train
Tanzania's Hassan sworn into office after deadly election violence
Powerful 6.3 quake kills at least 20 in Afghanistan, hundreds injured
Turkey set to call for action on Gaza as soon as possible, source says
