Some analysts, in Israel, Lebanon and other regional states, estimate the Iranian-backed Shiite movement has suffered "hundreds" of casualties in fighting rebel forces in recent weeks as the conflict moves toward what could be the decisive battle of the 27-month-old civil war.
Hezbollah is giving nothing away about the extent of its losses, but the analysts say the organization's large-scale deployment in Syria is steadily eroding its military capabilities.
For Hezbollah leader Sheik Hassan Nasrallah, there is "some good news for his involvement in Syria," observed Yoram Schweitzer, director the Terrorism and Low Intensity Warfare Project at the Institute for National Security in Tel Aviv.
"Hezbollah is gaining battle experience, but this is smaller in significance than the price Nasrallah's paying, politically and operationally. There's an erosion of Hezbollah's fighting forces and its resources.
"The organization's suffering a loss of personnel," Schweitzer noted. "Politically, this is increasingly chipping away at Hezbollah's image as the resistance party that fights the common enemy, Israel."
Mordechai Kedar, a Middle East expert at Bar-Ilan University's Begin-Sadat Center for Strategic Studies, says Hezbollah's casualty toll is a "big secret." But he estimated the number of killed and wounded is "in the hundreds."
There has been a steady body count since mid-2012 when large-scale Hezbollah deployment with Assad's forces began. But major casualties were suffered in the three-week battle for the strategic, rebel-held town of Qusair in western Syria that ended June 5 with a loyalist victory.
Lebanese sources say Hezbollah lost nearly 100 killed with double that number wounded out of some 1,500 men deployed.
The loss of Qusair, which gave Assad control of western Syria, helped convince U.S. President Barack Obama he had to start providing the disparate and fractious rebel forces with arms.
There have been scores of funerals for the fallen fighters in Hezbollah's Lebanese strongholds in recent weeks.
The casualties are causing concern among Lebanon's Shiites, and many other Lebanese, who lauded Hezbollah's war against Israel, eventually ending a 22-year-occupation of southern Lebanon in 2000, but are upset the group is now killing other Arabs and dragging Lebanon to the war.
Currently, Hezbollah is fighting with Assad's troops In Damascus, the Syrian capital where the rebels hold several districts. Syrian opposition officials say 34 Hezbollah fighters were killed in Damascus Saturday.
But the group's main force, said by military sources in Beirut to be 2,000- to 4,000 strong, is now building up around Aleppo, Syria's largest city and once its commercial heart.
The ancient city has been a battleground since the early days of the conflict that began in March 2011.
Hezbollah's fighters, reinforced by Iraqi Shiites of the Abu Fadi al-Abbas Brigade, are centered on the Shiite villages of Nubul and al-Zahraa northeast of Aleppo, which have become the staging area for attacks by Hezbollah and Assad's Syrian loyalists on the Minagh military airbase, a rebel strongpoint.
These forces' main mission is cutting the rebels' lines of supply and communication from neighboring Turkey, along which large shipments of weapons funded by Saudi Arabia and Qatar -- and more recently by the West -- are funneled.
"The disruption of rebel-held areas in the northern Aleppo governorate, particularly its logistics route from the Turkish border through the contested areas around Nubul and al-Zahraa to the front lines of Aleppo would be a significant blow to the armed opposition," said analyst Nicholas Heras of the Jamestown Foundation, a Washington think tank that monitors global security.
"Hezbollah's deepening involvement in the Syrian war is a high-risk venture," said Lebanese analyst Michael Young. "Many see this as a mistake by the party, and it may well be.
"Qusair will be small change compared to Aleppo, where the rebels are well entrenched and benefit from supply lines from Turkey. ...
"Hezbollah is willing to take heavy casualties in Syria, if this allows it to rescue the Assad regime," Young said.
But he stressed Hezbollah must avoid being dragged into a "long and debilitating campaign in Syria ... The party cannot allow Syria to become its Vietnam."
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