Hezbollah said on Saturday its top military commander, whose death it announced on Friday, was killed in Syria by Sunni Islamist artillery fire and not by an Israeli air strike as one member of the Lebanese Shi'ite movement had 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 (hardline Sunni) groups in the area," Hezbollah said in a statement.

The Shi'ite Muslim group is fighting in Syria, backing President Bashar Al Assad against a range of Sunni groups including Islamic State and the Al Qaeda-affiliated Nusra Front.

But a war monitoring group cast doubt on its version of Badreddine's death, saying there had been no shelling by rebels in that area for more than a week.

Damascus airport and its surroundings are controlled by the Syrian government and allied forces. Between it and government-held central Damascus, rebels control a portion of the Eastern Ghouta suburb, which has experienced fighting for most of the conflict now in its sixth year.

"There has been no recorded shelling or firing from the Eastern Ghouta area onto Damascus International Airport for more than a week," Syrian Observatory for Human Rights director Rami Abdulrahman told Reuters.

Hezbollah's statement did not say when the attack took place or when Badreddine died. Badreddine was given a military funeral in Hezbollah's stronghold in southern Beirut on Friday.

"The outcome of the investigation (into Badreddine's death) will increase our determination ... to continue the fight against these criminal gangs and defeat them," Hezbollah said.

Iran-backed Hezbollah, considered a terrorist group by the US and Gulf Arab states, wields enormous political influence in Lebanon alongside its powerful military wing.

Around 1,200 Hezbollah fighters are estimated to have been killed in the Syrian conflict.

ENEMIES

Badreddine had many enemies. He was sentenced to death in Kuwait for his role in bomb attacks there in 1983 and escaped from a Kuwaiti jail after Saddam Hussein's Iraq invaded in 1990.

His release from jail in Kuwait was one of the demands made by the hijackers of a TWA flight in 1985, and of the hijackers of a Kuwait Airways flight in 1988.

For years, Badreddine masterminded military operations against Israel from Lebanon and overseas and managed to escape capture by Arab and Western governments.

"The martyred commander spent years of his life on the front line of the jihad (struggle) against the Zionist entity," Iran's parliament speaker Ali Larijani said in a telegram to Hezbollah leader Sayyed Hassan Nasrallah reported by the group's media outlet Al Manar.

Israel declined to comment on speculation it was behind Badreddine's death, but a former Israeli official said his country would be glad of the news.

Badreddine was one of five Hezbollah members indicted by the UN-backed Special Tribunal for Lebanon in the 2005 killing of statesman Rafik Al Hariri, one of Lebanon's most prominent Sunni Muslim figures. Hezbollah denied any involvement and said the charges were politically motivated.

A Special Tribunal prosecutor described Badreddine as an elusive character who passed as an "unnoticed and virtually untraceable ghost through Lebanon".-Reuters