The coalition strikes reportedly occurred near al-Tanf town, where US' and British special operations forces have been training Syrian rebel fighters near the border with Iraq and Jordan.
"The strike did happen. It was against a pro-regime force operating in the vicinity of al-Tanf. This regime force was operating within a well-established de-confliction zone," the defense official told Sputnik.
The US defense official added that the US coalition commander considered the pro-Assad forces as a threat to coalition troops.
"The commander on the ground perceived this force to be a threat to coalition forces," the defense official said.
BREAKING: US official confirms to @BuzzFeedNews that the US-led Coalition hit Assad regime forces with air strikes in southern Syria today— Mike Giglio (@mike_giglio) 18 мая 2017 г.
The US-led coalition said that the agreement on a de-confliction zone with Russia remains in effect despite the strike on Syrian army.
The United States and Russia signed the bilateral memorandum of understanding in October 2015 to ensure their flight safety during combat missions over Syria.
On Monday, Al-Masdr News reported that Syrian Arab Army soldiers along and militias affiliated with the Iraqi Popular Mobilization Units are preparing to recapture the nearby Tanf Border crossing from Daesh.
In April, Daesh terrorists attempted to take the US base near At Tanf in which three US-backed Syrian rebels were killed.
This was not the first time the US-led coalition intentionally or accidentally struck the Syrian army fighting against Daesh. In the early hours of April 7, the United States launched 59 Tomahawk cruise missiles at the Syrian military airfield in Ash Sha’irat, located about 40 kilometers from the city of Homs. Moreover, on September 17, 2016, US-led coalition aircraft carried out four strikes against the Syrian army near the Deir ez-Zor airport, killing 62 soldiers and wounding some 100.