Syrian state media says Israel has launched an air strike against an army position south of the capital Damascus.
The Sana news agency said Syrian air defences had shot down two Israeli missiles in the Kiswah area on Tuesday.
It reported no casualties, but a monitoring group says at least nine pro-government forces had been killed, including Iranian-backed fighters.
Earlier on Tuesday, there were reports of loud explosions at a military base in the area.
A commander supporting President Bashar al-Assad told Reuters news agency that the strike had targeted a Syrian army position.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said the target was an arms depot.
The dead included members of the Iranian Revolutionary Guard and other Shia militiamen, it added.
Israel has not commented on the reports, but it has said it will stop what it considers Iran’s military “entrenchment” in Syria.
Iran has supported the Syrian government during the country’s seven-year civil war, deploying hundreds of military advisers and thousands of militiamen to the country.
It has reportedly built a military base in the area where Tuesday’s strike is said to have happened.
Last year, a Western intelligence source told the BBC that the Iranian military had established a compound at a site used by the Syrian army near Kiswah.
Iran has also vowed to avenge recent air strikes on its military facilities in Syria that were attributed to Israel.
Tensions between the two countries escalated on Tuesday when Israel said it had detected “irregular Iranian activity” in the occupied Golan Heights region of Syria.
It put the area, which is Syrian territory under Israeli control, under high alert and instructed bomb shelters to be unlocked.