"The Israeli strike killed six Iranian soldiers, including commanders, as well as the six members of Hezbollah. They were all in a convoy of three cars," AFP quoted a source close to Hezbollah.
The strike also killed six members of Lebanese military group Hezbollah.
According to the Hezbollah-affiliated al-Manar television channel, an Israeli helicopter fired missiles at a group of Hezbollah fighters as they "inspected" the town of Mazraat al-Amal in the Syrian Quneitra region on Sunday.
The air attack killed Jihad Mughniyeh, the son of a late military commander and Hezbollah field commander Mohammed Issa, who was in charge of the group's operations in Syria and Iraq.
The Lebanon-based Shiite paramilitary and political group has been active in Syria since the start of the Syrian conflict in 2011 and has allegedly been helping the Syrian government fight the Islamic State, a radical Sunni insurgent movement.