Israeli missiles targeted "military positions and intelligence facilities belonging to Iran and (pro-Iranian) militias" in the southern provinces of Daraa and Quneitra early on Wednesday, the Syrian Observatory for Human Rights said.
State media also reported on Wednesday that the "Israeli enemy launched an aggression" against military positions held by the government and its allies in Daraa province, without mentioning casualties.
The Observatory said on Thursday the strikes had killed six Iranians and three pro-regime Syrian fighters.
The Britain-based monitor gathers its information from a vast network of contacts across Syria.
Israel has carried out hundreds of airstrikes in Syria since the beginning of the conflict in 2011, targeting regime forces and those of its key allies Iran and Lebanese movement Hizballah.
It does not usually comment on specific reports of strikes, but does insist it has the right to defend itself by targeting positions held by Iran and its ally Hizballah.
The area targeted on Wednesday lies close to part of the Golan Heights that is occupied and annexed by Israel.
The Syrian conflict has killed more than 370,000 people and drawn in regional and world powers since it started with the brutal repression of anti-government protests.
On June 30, Israeli airstrikes killed six civilians, including three children, and nine mostly foreign pro-regime fighters, according to the Observatory.
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