“At least 27 pro-regime fighters were killed” in Thursday’s strikes, said Rami Abdel Rahman, director of the Britain-based Syrian Observatory for Human Rights.
He said “six Syrian soldiers and 21 foreign fighters, including 11 Iranians” were among the dead.
That updates the monitor’s initial toll of 23, which did not specify the number of Iranians.
“The new report is due to the death of wounded or missing persons whose deaths have been confirmed,” Abdel Rahman said.
Israel says it struck dozens of Iranian targets inside Syria early on Thursday in response to a salvo of rockets allegedly fired by Iranian forces into the Israeli-occupied Golan Heights.
Israeli Prime Minister Benjamin Netanyahu said Iran had “crossed a red line” and that Israel’s bombardment against targets in Syria was “a consequence”.
The Jewish state has long warned it will not accept Iran entrenching itself militarily in neighbouring Syria, where the Islamic Republic backs Assad’s regime in the country’s seven-year civil war.
Israeli forces have been blamed for a series of recent strikes inside Syria that have killed Iranians, though it has not acknowledged those raids.
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.
Fight against IS in Damascus stalls, dozens dead
At least 86 pro-regime fighters were killed in Syria over the past week in battles against the so-called Islamic State group as regime forces push to clear jihadists from their last stronghold in Damascus, a monitor said on Saturday.
The jihadists have lost 57 fighters in the clashes in the Hajar al-Aswad district on the outskirts of Damascus since May 5, according to the Britain-based Syrian Observatory for Human Rights.
Since mid-April, forces loyal to Syrian President Bashar al-Assad have pounded IS in its last Damascus bastion.
Retaking the area, which includes Hajar al-Aswad and the Palestinian refugee camp of Yarmuk, would place the regime in full control of the capital and its surroundings for the first time since 2012.
“The clashes continue. Despite its firepower, the regime has been unable to achieve any significant advance on the ground for a week,” Observatory director Rami Abdel Rahman said.
“IS is entrenched in tunnels and underground shelters and it has been conducting counter-attacks since Saturday.”
At least 203 pro-government fighters have been killed along with 159 IS jihadists since April 19, according to the Observatory.
Government forces have retaken 60 per cent of Hajar al-Aswad, but jihadists still control 80 per cent of Yarmuk, the monitor said.
Once a thriving district home to some 160,000 Palestinians and Syrians, Yarmuk’s population has fallen to just a few hundred people.
The regime continued to pound the area with air strikes and artillery fire on Saturday, the Observatory said.
IS has been expelled from most of the country since it declared a “caliphate” across large swathes of Syria and neighbouring Iraq in 2014.
But it still holds around five percent of Syrian territory, in eastern and central desert holdouts and on the edge of Damascus.
Syria’s war has killed more than 350,000 people since it started in 2011 with the brutal repression of anti-government protests before spiralling into a complex conflict involving world powers and jihadists.
