Reuters news agency quoted military and local sources as saying that unidentified planes targeted - on Monday - a base run by Iranian-backed armed factions in Deir Ezzor province in eastern Syria near the Iraqi border, where Tehran expanded its military presence last year.
Military sources and residents of the area said that the strikes took place south of the town of Al-Mayadin on the Euphrates River, which has become a large base for a number of armed Shiite factions, most of them from Iraq, since the expulsion of ISIS fighters nearly four years ago.
Two residents reported that the fighters of the Iranian-backed armed factions who were roaming the streets were put on high alert, and that ambulances were seen speeding towards the desert outskirts of the city after hearing several explosions.
A resident, Ahmed al-Shawi, told Reuters - in a text message - that "terrified elements of the Iranian militias are asking pedestrians and car owners to evacuate the city center."
Residents and military sources say that armed factions are now controlling the town, which is dominated by Sunni tribes, as part of their growing presence in Deir ez-Zor governorate.
There was no mention of the air attacks yet in the Syrian state media, which previously denied the deployment of thousands of fighters of Iran-backed armed factions in large parts of the country.
Israel, concerned about Iran's growing regional influence and military presence in Syria, says it has carried out hundreds of strikes in Syria to slow Tehran's consolidation of its position there.
Over the past year, Israeli drone strikes have focused on the border town of Al-Bukamal - southeast of Al-Mayadeen - which is located on a strategic supply route to the Iranian-backed armed factions, which regularly send reinforcements from Iraq to Syria.
These factions also control large areas of the border on the Iraqi side.
Western intelligence sources say Israel has expanded its air strikes on suspected arms transfers and deployments by Iran-backed militias and their Lebanese Hezbollah allies, who support Syrian President Bashar al-Assad.