Hezbollah commander Mustafa Amine Badreddine killed
Mustafa Amine Badreddine died in a large explosion near Damascus airport, the Lebanon-based militant group said in a statement on its al-Manar website.
Badreddine is charged with leading the assassination of former Lebanese PM Rafik Hariri in Beirut in 2005.
Hezbollah supports Syria's President Bashar al-Assad and has sent thousands of fighters into Syria.
The US treasury, which imposed sanctions on Badreddine last July, said at the time he was "responsible for Hezbollah's military operations in Syria since 2011, including the movement of Hezbollah fighters from Lebanon to Syria, in support of the Syrian regime".
Lebanon's al-Mayadeen TV had earlier said that Badreddine, 55, died in an Israeli air strike. Israel has not commented on the claim.
Announcing Badreddine's death, Hezbollah said in an initial statement: "He took part in most of the operations of the Islamic Resistance since 1982," referring to the group's military wing.
The second statement, on al-Manar's website, said: "The investigation will work on determining the nature of the explosion and its causes and whether it was a result of an air, missile or artillery attack.
"We will announce further results of the investigations soon."
Al-Manar said he would be buried in Beirut on Friday afternoon.
Source: bbc.com