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.
The Pentagon is expected to send thousands of soldiers from the army's elite 82nd Airborne Division to the Middle East, according to reports on Tuesday, adding to the massive military buildup even as the Trump administration seeks talks with Iran.
A rare Russian daytime drone attack on Ukraine killed three people, wounded several dozen and set a building in the historic centre of the western city of Lviv aflame on Tuesday, officials said, following an overnight bombardment that killed five.
The Ministry of Defense (MoD) have offered their condolences to the family of a Moroccan civilian contractor in the UAE Armed Forces who was killed during a routine mission in Bahrain following an Iranian missile attack.
There is no direct Qatari mediation between the United States and Iran, but Doha supports all formal and informal diplomatic channels to end the war, Qatar's foreign ministry spokesperson said on Tuesday.
Germany and France have both spoken out against United States President Donald Trump's actions over the conflict in Iran in a rare rebuke of a major ally.