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.
President Donald Trump said on Friday the US was getting very close to meeting its objectives as it considers winding down its military efforts in the Iran war and called on countries that use the Strait of Hormuz to guard and police it "as necessary".
The Israeli military said early on Saturday it was striking Hezbollah targets in Beirut, after issuing an evacuation warning for seven neighbourhoods in the southern suburbs of the Lebanese capital.
The US military is deploying thousands of Marines to the Middle East, officials told Reuters on Friday, as President Donald Trump accused NATO allies of cowardice over their reluctance to send forces to help open the Strait of Hormuz.
A fire that broke out around lunchtime on Friday at a car parts factory in the South Korean city of Daejeon on Friday, has left 10 people dead, 25 seriously injured and 34 with minor injuries, the country's safety ministry said on Saturday.
The Kuwait Petroleum Corporation (KPC) has announced that the Mina Al-Ahmadi Refinery, operated by Kuwait National Petroleum Company (KNPC), came under drone attacks early on Friday, with a fire breaking out at several units as a result.