Islamist extremists killed military chief in Syria: Hezbollah

The Iran-backed movement has deployed thousands of fighters in Syria where Mustafa Badreddine had led its intervention in support of President Bashar al-Assad.

"An investigation has shown that the blast that targeted one of our positions near the Damascus international airport that led to the martyrdom of the brother commander Mustafa Badreddine was caused by artillery bombardment carried out by takfiri (Sunni extremist) groups present in that region," a Hezbollah statement said.

It did not name any particular group and there has been no claim of responsibility for the attack.

Hezbollah has been battling opponents of the regime including Sunni extremists from the Islamic State jihadist group and Al-Nusra Front, Al-Qaeda's Syria affiliate.

A Syrian security source has told AFP that Badreddine was in a warehouse near the Damascus airport when it was rocked by a blast on Thursday night.

No aircraft was heard before the explosion, the source said.

In its statement today, a day after thousands attended Badreddine's funeral in Beirut, Hezbollah vowed no let up in its war against those it describes as "criminal gangs" in Syria.

"The result of the investigation will only increase our determination and will to pursue the fight against those criminal gangs until they are defeated," the statement said.

"It is the same battle against the American-Zionist scheme in the region, which the terrorists are spearheading," it added.

Badreddine was on a US terror sanctions blacklist, was a key suspect in the 2005 assassination in Beirut of Lebanese ex-premier Rafiq Hariri and was one of the "most wanted" by Israel.

His predecessor, cousin and brother-in-law Imad Mughniyeh, was killed in Damascus in a 2008 bombing that Hezbollah blamed on its regional arch-foe Israel with whom it has fought several wars.

Badreddine's death has raised many questions, namely because the area where he was killed is technically under the control of the Syrian army while Hezbollah and Iranian fighters are also present there.

The closest rebel positions are seven kilometres (four miles) away in the Eastern Ghouta area.