Late night airstrikes in eastern Syria along the border with Iraq have targeted Iran-backed militiamen, inflicting casualties, Syrian opposition activists say.
According to two paramilitary officers in Iraq, some of those killed in the attack were Iranian nationals.
It was not immediately clear who was behind the strikes.
The US military, which along with Israel has carried out such strikes in the past, said it was not behind them and had no involvement in the al-Qaim attack. The Israeli army refused to comment on the incident.
The airstrikes, shortly before midnight on Tuesday, hit tanker trucks carrying fuel and other trucks carrying weapons for the militias in Syria's eastern province of Deir el-Zour, according to the Britain-based Syrian Observatory for Human Rights, an opposition war monitor.
It added that at least 14 people, most of them militiamen, were killed in the strike.
The Deir Ezzor 24, an activist collective, reported three airstrikes targeting Iran-backed militias in the Syrian border town of Boukamal and nearby areas. It had no immediate word on casualties.
Earlier, members of Iraqi paramilitary groups operating in the area said an airstrike on a convoy carrying fuel across the Iraqi border into Syria killed at least 10 people late on Tuesday.
The strike hit a convoy of about 15 trucks that had crossed into Syria near the town of al-Qaim, two paramilitary officers told The Associated Press.
It was unclear where the convoy was coming from, but the officers said some of those killed were Iranian nationals.
Iranian state television's English-language service, Press TV, early on Wednesday cited unnamed sources claiming there was an attack on a fuel truck convoy crossing from Iraq into Syria at the al-Qaim border crossing.
Press TV claimed the convoy was carrying Iranian oil to Lebanon through Syria. Iranian officials offered no casualty details.
Iran's state TV claimed the convoy attack was warried out by US drones and helicopters, offering no evidence for the claim. It said the convoy included 22 tanker trucks, adding that the attack took place after eight of the trucks crossed into Syria.
The US military denied this. Army Major Rachael L. Jeffcoat told the AP on Wednesday that "no US forces or US-led coalition (members) conducted an airstrike in al-Qaim, Iraq, on the border with Syria.