United States warplanes have struck pro-Syrian government forces that were said to pose a threat to American troops and allied rebels operating near the border with Jordan.
Misidentifying Syrian forces for Islamic State fighters, American and coalition warplanes dropped more than 30 bombs and fired more than 300 rounds for almost a half-hour during the September 17 attack near the eastern Syrian city of Deir al-Zour before Russian commanders alerted their US counterparts to their mistake.
There were no immediate details on any civilian injuries.
A CNN reporter in Washington that was briefed by USA officials said a convoy of 20 pro-regime vehicles was headed toward Al-Tanf on Wednesday vehicles, searching vehicles and buildings along the way.
The strike took place in At Tanf near Syria's border with Jordan and Iraq, the official said.
With a mission that focuses completely on ISIS, US troops have rarely had to worry about operating in close proximity to Syrian forces and their aligned militias.
The U.S. -backed forces in that area are fighting against Islamic State militants.
Attempts to stop the convoy included a call to the Russians - who are working with the Syrian regime - then a "show of force" in the skies above the vehicles, followed by warning shots. The Russians relayed the message to the Syrian government, but the forces did not withdraw, the official said.
"The Syrian Arab Army is fighting terrorism on its territory, and no party has the right to determine the course of its operations", a source told AFP. When the Syrians insisted on proceeding into the area, the USA planes were cleared to fire.
More than 400,000 people have so far been killed in the conflict which also triggered one of the world's worst refugee and humanitarian crisis with millions of people displaced.
Said Seif, an official with the Western-backed Free Syrian Army Shahid Ahmed Abdo rebel group, said the United States intervention will help the rebels to hold their ground against any future incursions by the army and its Iranian backed militias.
President Bashar al-Assad's army is trying to prevent US-backed forces from leading that fight.