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.
An Iranian Revolutionary Guards senior official said on Monday that the Strait of Hormuz is closed and Iran will fire on any ship trying to pass, Iranian media reported.
Bahrain’s National Communication Centre says the country's defence force has repelled a new wave of attacks targeting the kingdom, intercepting and destroying 70 ballistic missiles and 59 Iranian drones.
Qatar’s Ministry of Defence says its armed forces have shot down two Iranian aircraft and intercepted multiple missiles and drones targeting the country.
Kuwait's air defences mistakenly shot down three US F-15 fighter jets during active combat on Monday, US Central Command said on Monday, describing it as an apparent friendly‐fire incident during the conflict with Iran.
Gaza is rapidly running out of its limited fuel supply and stocks of food staples may become tight, officials say, after Israel blocked the entry of fuel and goods into the war-shattered territory, citing fighting with Iran.