A missile attack by an unidentified aircraft hit a position near a Syrian government-held town along the Iraqi border overnight on Tuesday, reportedly killing at least 10 Iran-backed fighters.
The attack took place in Al Bukamal, in the eastern Syrian province of Deir Az Zor, security officials said.
Reuters news agency reported the raid was carried out by unmanned aerial vehicle. However, according to the report, it caused no casualties.
The missile hit a weapons depot belonging to Iraqi factions operating under the banner of the Popular Mobilization Forces, the name given to mainly Shia militias in Iraq that are backed by Iran.
The Britain-based Syrian Observatory for Human Rights and Deir Ezzor 24, an activist collective, said 10 fighters were killed. Iraqi officials confirmed the death toll to the Associated Press news agency.
It was the latest in a series of unclaimed attacks inside Iraq and along the border with Syria targeting Iran-backed militias. Last week, unknown warplanes targeted an arms depot and Iranian-backed militia posts in Al Bukamal, killing at least 18 fighters.
A Syrian security official said Israeli jets were behind Tuesday's attack, but denied there were casualties.
Israel frequently hits Iranian targets in war-ravaged Syria and appears to have recently expanded its campaign. It has said it will not allow the Iranians, who support forces of Syrian President Bashar al-Assad, to establish a permanent military presence in Syria.
Iran-backed forces, including Lebanon's Hezbollah militia, played a major role in recovering Al Bukamal from the Islamic State of Iraq and the Levant (ISIL or ISIS) in late 2017. The border crossing to Iraq, however, remains closed.