BEIRUT: The American military denied responsibility for a drone strike that killed at least eight Hezbollah fighters in eastern Syria Monday, after a pro-party media outlet claimed the U.S. was responsible. “The DoD did not strike Hezbollah today,” a spokesman for the U.S. Department of Defense’s Syria office told The Daily Star. Later, U.S. Army Col. Ryan Dillon – spokesperson for Operation Inherent Resolve, the U.S.-led coalition against Daesh – also denied the strike was carried out by the coalition, in a statement via Twitter. “Strikes reported E[ast] of Palmyra #Syria killing 7 Hezbollah is NOT #CJTFOIR [Combined Joint Task Force – Inherent Resolve] area of [operation]. Our fight is with #ISIS; #Raqqa & E[ast] of Euphrates.”

Lebanese security sources told The Daily Star that Monday’s incident brings Hezbollah’s death toll in Syria to at least 24 since Sept. 28. In a statement Monday evening, the Syrian Observatory for Human Rights – a U.K. based monitoring group – placed the Hezbollah death toll at 32 in the same timeframe.

Early Monday morning, pro-Hezbollah website Mulhak quoted a Hezbollah source saying an unmanned U.S. drone had struck a base in Syria, killing eight fighters and wounding 15 others. “American rockets hit a Hezbollah base in Syria’s eastern Homs countryside,” the source reportedly told the website.

While a Hezbollah source confirmed, “eight [fighters] were martyred today [Monday],” he refused to elaborate on the circumstances.

The Britain-based Syrian Observatory of Human Rights also reported the incident, saying it took place south-west of Deir al-Zor province near the Iraqi border where regime allied forces have been battling Daesh. But it did not identify the country operating the drone. Unmanned aerial vehicles are commonly used over the Syrian battlefield by a number of different forces, including non-state groups.

Reuters news agency did not rule out Russian “friendly fire” was to blame for the deadly incident.

A separate Hezbollah source said late Monday that the death toll hadn’t risen from eight, despite reports by the Syrian Observatory that the death toll had hit 10. Hezbollah quickly revised the initial death toll of seven after announcing that Ahmed al-Aashek, a Hezbollah field commander, had been killed. The party gave no further details.

In a statement early afternoon, the Observatory said that “other fighters were injured and some were severely injured, potentially leading to an increase in the number of deaths,” adding that the strike took place south-east of the town of Sukhneh.

While Israel has regularly conducted strikes on suspected Hezbollah positions and weapons shipments, the involvement of the U.S. – if confirmed – would prove a watershed incident in the yearslong conflict. The majority of Israel’s strikes have been in western or southern Syria, near its own borders.

The U.S. has hit struck pro-Damascus forces in Syria on a number of occasions, although many of these it has cited as mistakes. In September 2016, the U.S. admitted that an air raid it believed was targeting Daesh had in fact hit and killed at least 62 Syrian soldiers and wounded over 100 others. On April 7, U.S. President Donald Trump ordered a salvo of 59 Tomahawk cruise missiles on the Syrian government’s Shayrat Airbase in response to a chemical attack on the town of Khan Shaykhun.

Hezbollah intervened in Syria near the start of the ongoing war to prop up the embattled Assad government and has been one of the most capable ground forces, despite losing hundreds of fighters.