Air strikes against positions belonging to regime forces and Iran-backed militias in east Syria on Saturday killed six fighters as the new head of Tehran's elite Quds force reportedly visited the battlefield.
Four Syrian nationals were among those killed in the raids on Al Abbas village near the border with Iraq, said the Britain-based Syrian Observatory for Human Rights.
It was not immediately clear if they were soldiers with the Syrian army.
The war monitor did not confirm who was behind the attack but said Israel was "likely responsible".
Israel has launched hundreds of strikes in Syria since the start of the civil war in 2011.
It has hit government troops, allied Iranian forces and fighters from Hezbollah.
Israel rarely confirms details of its operations in Syria, but says Iran's presence in support of President Bashar Al Assad is a threat and that it will continue its strikes.
Last week, Israeli strikes in the eastern province of Deir Ezzor and the southern province of Suweida killed seven fighters, including two Syrian soldiers.
The latest strikes came as an Iranian news agency made a rare albeit brief announcement that Islamic Revolutionary Guard Corps Quds Force head Gen Esmail Qaani visited the Syria front.
Gen Qaani replaced Qasem Suleimani, the country’s notorious shadowy militia commander who directed a network of allied fighting groups in conflicts across the Middle East, after he was killed in a US air strike near Baghdad airport in January.
Iran's semi-official Tasnim news agency reported Gen Qaani had visited Albukamal, a Syrian town on the border with Iraq, in the past few days. It later deleted the report without explanation. Other Iranian news media made no mention of the visit.
Tasnim quoted Gen Qaani as describing ISIS fighters as agents of Israel and the US, a common accusation by Iran.
The Quds Force under Suleimani was instrumental in directing militia that fought on behalf of the Syrian president throughout the nine-year Syrian war.
On Saturday, Iranian media said the bodies of two IRGC members killed in Syria four year ago were repatriated after being recently found and identified.
The war in Syria since 2011 has killed more than 380,000 people and displaced more than half of the country's pre-war population.