Hizbollah’s intervention in Syria has been vital to the battlefield successes of president Bashar Al Assad’s government and boosted the militant group’s prestige as a fighting force.
But these gains have come at a cost: in just four years Hizbollah has likely lost as many fighters as it did in its decades of conflict with Israel. Meanwhile, its senior commanders have been left exposed as the group morphs from a guerrilla force into a conventional army fighting in a foreign land.
Since the Lebanese Shiite militants entered the war in Syria, they have lost at least six high-profile commanders. Two - Samir Kuntar and Jihad Mughniyeh - are believed to have been assassinated in Israeli air strikes. Hizbollah also blamed the 2013 assassination of military commander Hassan Al Laqqis in Beirut on Israel, though a previously unknown Sunni militant group claimed responsibility. Other commanders were killed in battles with extremist factions.
The latest to fall was Mustafa Badreddine, Hizbollah’s top military commander who was running the group’s war in Syria. Hizbollah announced his death on May 13 and eventually said he was killed near Damascus airport in an artillery attack carried out by Sunni extremist groups.
However, many have been widely sceptical of Hizbollah’s claims, with the Syrian Observatory for Human Rights saying that no shelling occurred in the area near the airport and no rebel group claiming responsibility for the killing.
“It’s very clear that all the recent assassinations - or at least the big ones - are happening in Syria. So whatever control mechanisms they have seem to be working in Beirut but not in Syria," said Randa Slim, a Hizbollah expert with the Washington-based Middle East Institute.
Ms Slim added that the Syrian government is perhaps more prone to penetration by foreign intelligence agencies, providing room for lapses that could put Hizbollah fighters at risk.
“The war in Syria is uncharted territory for Hizbollah, logistically and operationally," said Bilal Saab, a fellow at the Washington-based Atlantic Council. “They have learned a lot since the beginning of the conflict, but the risks are still considerable, including operational security. When you work with foreign entities such as Syrian troops and other militias, there is always a chance of moles and spies wreaking havoc from within."
Amal Saad-Ghorayeb, a professor at Beirut’s Lebanese University who is seen as close to Hizbollah, said the group’s presence in Syria has left its top-ranking commanders fully exposed to attacks from Israel and extremist rebel groups.
Alongside fighting in Syria, Hizbollah is also battling Jabhat Al Nusra and ISIL along Lebanon’s border with Syria and continues to stare down its archenemy, Israel.
The group “is overstretched and it is going to expose it to more attacks", said Ms Saad-Ghorayeb.
It is difficult to determine how much the group’s losses in Syria have affected its overall strength. Hizbollah is tight-lipped and commanders like Badreddine and Imad Mughniyeh - the group’s former military commander who was assassinated in a 2008 car bombing in Damascus - spend their lives in the shadows, their actions and even faces only really known in death. Even determining how many key commanders the group has is difficult.
“We don’t know how many senior members of the military are out there," said Aurelie Daher, Hizbollah expert and author of the book Hezbollah: Mobilization and Power. “If they have lost a dozen of them, then yes, they have lost many officials. If they have a hundred or more, then one can consider their losses in this regard as less important. Everything is relative."
What is known is that key leaders like Imad Mughniyeh and Badreddine rose through the ranks of Hizbollah in its early days, and have participated in all of the group’s major military actions. They are men who went from orchestrating bombings at home and abroad to eventually commanding armies.
“There is an institutional knowledge, an institutional expertise that can only be accumulated over years of working in the field in Lebanon and abroad," said Ms Slim, the Middle East Institute expert. “I think people like Imad Mughniyeh, like Badreddine, these lie at the core of the operation. If these are eliminated, a lot of institutional know-how goes away with them."
Finding replacements with the experience and charisma of these kinds of leaders can be difficult, she added.
“We are talking here about commanders who are also military strategists and are responsible for outlining Hizbollah’s military strategy in these various arenas," said Ms Saad-Ghorayeb.
But despite their importance, she says Hizbollah does not rely on personality cults and has grown into a large military force with the ability to mobilise tens of thousands of reservists. At home, it has also grown into a movement that acts more like an institutionalised and evolving state.
“I think it will keep adapting to changing military and political realities," Ms Saad-Ghorayeb said. “It’s not just going to freeze now because an important commander was assassinated."
Israel appears to be taking advantage of Hizbollah’s deployment in Syria to isolate and assassinate the group’s leaders there - either because it is easier to do so in Syria or because they feel repercussions are less likely. But despite this, Ms Daher says Hizbollah still holds major manpower and leadership assets in Lebanon in case Israel were ever to attempt an attack on the group’s homeland.
Based on her conversations with contacts in the movement, Ms Daher said: “Hizbollah is perfectly aware that there is a risk that Israel would take advantage of the situation to hit the party on its own territory, in Lebanon."
“A large number of fighters and military senior officials were hence left at home for that purpose. The elite squads are still in Lebanon."