A pro-Iran commander was among three killed in drone strikes near Al Bukamal in Syria on Monday, the Britain-based Syrian Observatory for Human Rights said, only hours after strikes that killed seven others the previous evening.
"A commander in an Iran-backed group and two of his companions, all of them non-Syrian, were killed this morning after renewed drone strikes," the war monitor said on Monday.
An Iraqi border guard in the frontier city of Al Qaim confirmed he heard an explosion rock the nearby Syrian city of Al Bukamal but could not confirm if it was an attack or a controlled blast.
The seven who were killed the previous night were “drivers and their assistants, all of them non-Syrians”, the Syrian Observatory for Human Rights said. They were “killed as a result of unidentified aircraft targeting a convoy of Iran-backed groups last night”, it added.
No group has claimed responsibility for the attacks, although the Iraqi-Syrian border area has been the site of several US and Israeli air strikes against Iran-backed militias.
Iraqi and Lebanese militias, supported by Tehran, have established a foothold in Syria while fighting in support of President Bashar Al Assad during the civil war that began in 2011. The war against ISIS between 2014 and 2017 further bolstered their positions.
Iraqi militias deployed near the Al Qaim border crossing on the Iraqi side and inside Syrian territory say their presence is essential to protect the borders.
Iran has used Al Qaim to move weapons, including missile systems, and supply Lebanon with fuel to alleviate pressure on the country's struggling electricity grid.
Al Bukamal is an agricultural town on the Euphrates river in the south-eastern corner of Syria, where Russian forces and the US army have co-existed since 2015, partly because they had set up "deconfliction" channels to avoid clashes between the two militaries.
A Russian command centre, for example, is slightly north of the US sphere of influence in the Tanf region south of Al Bukamal.
Pro-Iranian militias are also active in the south-east, as well as ISIS remnants and small rebel groups opposed to President Bashar Al Assad. Syrian security forces also maintain a presence and are nominally in charge of the border.
Sources in the Syrian opposition to Mr Al Assad say Albu Kamal is the main transit point for a host of contraband from Iraq to Syrian regime areas.
They say the shipments include weapons originating from Iran to Hezbollah in Lebanon or pro-Iranian militia in Syria, which that have made the convey targets of regular air strikes.
On other occasions, the shipments consist of spare parts, smuggled Iraqi diesel, or raw material for Captagon factories near Damascus.