Mustafa Badreddine's death is seen as a significant blow to the Assad regime
A senior Hezbollah military commander - Mustafa Badreddine - has been killed in an attack in Syria.
The 55-year-old died in an explosion targeting one of the Shia militant group's bases near Damascus airport.
Badreddine led Hezbollah's intervention in Syria supporting President Bashar al-Assad - and his killing is seen as a significant blow to the regime.
The Lebanon-based group said: "According to preliminary reports, a large explosion targeted one of our positions near Damascus international airport killing brother commander Mustafa Badreddine and wounding other people.
"He said months ago that he would not return from Syria except as a martyr or carrying the flag of victory."
It is not known whether Badreddine was killed by an air raid, missile attack or artillery shelling - or who launched the assault.
Lebanese TV station al-Mayadeen earlier reported he was killed in an Israeli attack. Israel declined to comment.
Badreddine was known for masterminding military operations against Israel from Lebanon and overseas.
He was once dubbed by a prosecutor of the International Criminal Court as an "untraceable ghost".
The militant commander was one of four figures from the organisation accused of the assassination of Rafic Hariri, the former prime minister of Lebanon, in February 2005.
The trial began in his absence last year at The Hague in the Netherlands.
Badreddine was also suspected of involvement in the 1983 bombings of the US and French embassies in Kuwait and was sentenced to death, but escaped from prison after Saddam Hussein's Iraqi forces invaded the country in 1990.
Hezbollah, which is listed as a terrorist group by the US, has been very active in Syria helping Assad's war against Sunni rebels.
His killing is the biggest blow to the militant group since the 2008 assassination of his predecessor, Imad Mughniyeh, who died in a bomb attack in Damascus.
It comes as a fragile truce in Syria's five-year conflict teeters on the brink of collapse.