Lebanese Shia group says explosion in Shebaa Farms area was to avenge killing of its commander Samir Kantar last month.
Top Hezbollah commander Mustafa Badreddine was killed in Syria this week, the Lebanese Shia group has said.
“He took part in most of the operations of the Islamic resistance since 1982,” Hezbollah said in a statement on Friday, announcing his death and describing him as a “great jihadi leader”.
Badreddine, 55, was one of the highest ranking officials in the group, and believed by the US government to be responsible for Hezbollah’s military operations in Syria, where it is fighting alongside Syrian President Bashar al-Assad.
He was killed on Tuesday night, the statement said, adding that the attack targeted one of Hezbollah’s bases near Damascus airport, the group’s nerve-centre in the Syrian capital.
On Friday, thousands of Hezbollah supporters carried the coffin of Badreddine, draped in a Hezbollah flag, during his funeral procession in a southern suburb of Beirut.
The group said it was working to “define the nature of the explosion and its cause, and whether it was the result of an air strike, or missile [attack] or artillery”.
Mustafa Badreddine replaced his brother-in-law Imad Mughniyah after the Hezbollah commander was killed in a car bombing in Damascus in 2008.
Israel officially denied being behind Mughniyah’s killing, but Israeli media reported at the time that the Hezbollah commander had been a target of Israeli assassination attempts since the 1990s.
Accounts cited by the Jerusalem Post stated that Mughniyah was assassinated by Israeli intelligence agents in revenge for the 2006 Lebanon War.
Earlier on Friday, the Lebanese TV station Al Mayadeen reported that Badreddine had also been killed in an Israeli attack.
However, there was no immediate response from Israel, which has attacked Hezbollah targets in Syria several times during the country’s five-year conflict.
“We decline to comment,” an Israeli military spokeswoman said.
Al Jazeera’s Zeina Khodr, reporting from Beirut, said Badreddine was the highest-ranking Hezbollah commander to have been killed in Syria since the conflict began five years ago.
“Some Hezbollah sources are saying that when Imad Mughniyah was killed, he was not replaced by just one man, Badreddine, but rather by several men. Nonetheless, Badreddine was a very high-ranking figure in the organisation.
“Hezbollah has suffered heavy losses in Syria, with some sources estimating that at least 1,200 fighters have died since the group started its involvement in the war. The group is weakened and some in Lebanon are wondering what Hezbollah’s exit strategy is.
“Hezbollah’s military intervention in Syria caused a divide in Lebanon. Some say it was totally wrong as it exposed Lebanon to threats. However, Hezbollah sees this as an existential decision because the Syrian government provides a lifeline to the group.”
Badreddine was indicted by the United Nations-backed Special Tribunal for Lebanon over the 2005 killing of a former prime minister, Rafik al-Hariri, and was also sanctioned by the United States.
Badreddine was sentenced to death in Kuwait for his role in bomb attacks there in 1983. He escaped from prison in Kuwait after Iraq, under the leadership of Saddam Hussein, invaded the country in 1990.
Mathew Levitt, a senior fellow at the Washington Institute and the author of Hezbollah: The Global Footprint of Lebanon’s Party of God, told Al Jazeera that Badreddine’s killing would hurt the group.
“This is a pretty significant blow to Hezbollah … He was extremely close to the Secretary General of Hezbollah Hassan Nasrallah,” Levitt said.