Hezbollah’s top military commander in Syria, Mustafa Amine Badreddine, was killed in artillery fire by jihadists, the Lebanese group says.
Badreddine’s death near Damascus airport was announced on Friday and initially blamed on Israel, Hezbollah’s chief enemy.
Badreddine was believed to have run all Hezbollah’s military operations in Syria since 2011.
Thousands of Hezbollah troops are supporting President Bashar al-Assad.
This has pitted it against several groups of anti-Assad rebels – from so-called Islamic State (IS) to the al-Nusra Front.
Without naming any group, the Hezbollah statement said: “Investigations have showed that the explosion, which targeted one of our bases near Damascus International Airport, and which led to the martyrdom of commander Mustafa Badreddine, was the result of artillery bombardment carried out by takfiri groups in the area.”
Takfiri is used to describe militants who believe Muslim society has reverted to a state of non-belief.
However, the BBC’s Arab Affairs Editor Sebastian Usher says questions still remain over Badreddine’s death.
A monitoring group, the Syrian Observatory for Human Rights, said there had been no recorded shelling or firing in the area for more than a week, although Hezbollah has not said when Badreddine died.
Many political assassinations involving Lebanese and Syrian political figures have remained unsolved, our correspondent says.
The Lebanese Shia Islamist movement has played a major role in helping Iran, its main military and financial backer, to prop up the government of President Assad since the uprising erupted in 2011.
Thousands of Hezbollah fighters are assisting government forces on battlefields across Syria, particularly those near the Lebanese border, and hundreds are believed to have been killed.
The Hezbollah statement said Badreddine’s death “will increase our determination… to continue the fight against these criminal gangs and defeat them”.
Born in 1961, Badreddine is believed to have been a senior figure in Hezbollah’s military wing. He was a cousin and brother-in-law of Imad Mughniyeh, who was the military wing’s chief until his assassination by car bomb in Damascus in 2008.
According to one report, a Hezbollah member interrogated by the Canadian Security Intelligence Service (CSIS), described Badreddine as “more dangerous” than Mughniyeh, who was “his teacher in terrorism”.
They are alleged to have worked together on the October 1983 bombing of the US Marine Corps barracks in Beirut that killed 241 people.
Badreddine is reported to have sat on Hezbollah’s Shura Council and served as an adviser to the group’s overall leader Hassan Nasrallah.
The group was established in the wake of the Israeli occupation of Lebanon in the early 1980s, and has called for the “obliteration” of Israel.
Badreddine was also charged with masterminding the assassination of former Lebanese PM Rafik Hariri in Beirut in 2005.
An indictment from the ongoing Special Tribunal for Lebanon in The Hague details Badreddine’s role in bombings in Kuwait in 1983, that targeted the French and US embassies and other facilities, and killed six people.
He was sentenced to death over the attacks, but later escaped from prison.