The chief of Syria's air defence forces, General Hussein Ishaq, has been killed in combat near Damascus, a security official has told news agencies.
The general died on Saturday of wounds suffered when rebels attacked Syrian air defence headquarters near the town of Mleiha, a key battleground southeast of the capital.
He is one of the few top-ranking officers whose deaths have been announced during Syria's three-year war.
The army's entire arsenal and forces are deployed in Damascus's war against rebels seeking to overthrow President Bashar al-Assad, whose regime brands the uprising as a foreign-backed "terrorist" plot.
"The regime's air defence force is to face a possible US attack, but in this war it is using its firepower against the rebels," Syrian Observatory for Human Rights director Rami Abdel Rahman told AFP.
Abdel Rahman called Ishaq's death an "important psychological blow" to the regime.
For more than a month, the army backed by the Lebanese Shia group, Hezbollah, has been battling to recapture Mleiha, a strategic rebel bastion.
Mleiha has been under siege for more than a year, and under near-constant bombardment for more than a month.
The UK-based Observatory, an anti-government monitoring group, said that despite initial regime advances in Mleiha, the rebels have recovered ground, retaking several buildings around the central town hall.
While the army remains in control of Damascus, rebels still hold a number of towns and villages on the outskirts, despite a suffocating blockade and frequent air strikes and shelling.