Israeli army footage of Thursday's attack shows the targetting of a Syrian missile launcher (screengrab)
At least 11 Iranians were among those killed in unprecedented Israeli strikes on Syria this week, an activist group said on Saturday.
The UK-based Syrian Observatory for Human Rights said at least 27 pro-Syrian fighters were killed on Thursday when Israeli jets hit targets in Syria.
"Six Syrian soldiers and 21 foreign fighters, including 11 Iranians" were among the dead, said the group's director, Rami Abdel Rahman.
The observatory initially reported 23 killed in the strikes and did not specify their nationality. "The new report is due to the death of wounded or missing persons whose deaths have been confirmed," Abdel Rahman said.
The strikes dramatically ramped up tensions in the region days after US President Donald Trump announced a withdrawal from an international deal that had aimed at easing tensions between Iran and the West.
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Israel said it destroyed nearly all of Iran's military infrastructure in the strikes which were launched in response to 20 missiles fired at the Israeli-occupied Golan Heights.
Israel blamed the Quds forces, a special detachment of the Iranian Revolutionary Guard, for being behind the missiles. Iran denied the accusation.
The Golan Heights are Syrian territory occupied by Israel in 1967 and annexed in 1981. The annexation has not be recognised by the international community.
"We hit nearly all the Iranian infrastructure in Syria," said Israeli Defence Minister Avigdor Lieberman, in a rare Israeli acknowledgment of strikes in Syria.
"They need to remember the saying that if it rains on us, it'll storm on them. I hope we've finished this episode and everyone understood."
Israel has long warned it will not accept Iran entrenching itself militarily in neighbouring Syria, where Tehran has deployed forces to support the government of President Bashar al-Assad in the country's seven-year civil war.
Iran condemns 'Israeli aggression'
Israeli forces have been blamed for a series of recent strikes inside Syria that have killed Iranians, though it has not acknowledged those raids.
But Thursday's air raid came amid heightened tension in the regime after President Trump announced on Tuesday that the US would withdraw from the 2015 Iran nuclear deal.
The deal, signed between Iran and world powers, including Russian and the United States, had eased economic sanctions on Iran in return for the country reducing its nuclear programme.
Trump had long threatened to withdraw from the accord, saying it was too easy on Iran.
All other signatories had sought to maintain the agreement. Israel however, which has long been concerned about Iranian influence in the Middle East welcomed Trump's decision.
Russia, which is also an ally of Assad, said on Thursday that Syria had shot down more than half of the missiles fired at it overnight by Israel.
It added that 28 Israeli fighter jets launched at least 60 missiles in Syria.
Iran condemned the Israeli air raid on Friday and said Syria had the right to defend itself against Israeli aggression.
"Iran strongly condemns … [Israel's] attacks on Syria. The international community's silence encourages Israel's aggression. Syria has every right to defend itself," state TV reported foreign ministry spokesman Bahram Qasemi as saying.
Israel says it has conducted dozens of operations in Syria to stop what it says are advanced arms deliveries to one of its main foes, Iran-backed Hezbollah.