Israel said it would not comment on the attack, but Iranian officials vowed a stiff response, with fears of even further violence between Israel and Iran's allies amid the Gaza war.
Iran's Islamic Revolutionary Guard Corps named Brigadier General Mohammad Reza Zahedi and another high-ranking officer, Brigadier General Mohammad Hadi Haji Rahimi, as among seven of its members killed.
Britain-based war monitor the Syrian Observatory for Human Rights said 11 people, including several Guards members, were killed when "Israeli missiles... destroyed the building of an annex to the Iranian embassy".
The toll includes "eight Iranians, two Syrians and one Lebanese -- all of them fighters, none of them civilians," Rami Abdel Rahman, who heads the Observatory with a network of sources in Syria, told AFP.
Iran's ambassador to Syria, Hossein Akbari, told Iranian state TV that the attack "was carried out by F-35 fighter jets" that fired six missiles at the building.