"The #Coalition does not seek to fight Syrian regime or pro-regime forces", coalition spokesman Army Col. Ryan Dillon wrote on Twitter.
Dillon said that earlier in the day, the US had carried out another strike against pick-up trucks carrying weapons that had moved against USA -backed fighters near the town of At Tanf.
The pro-Assad alliance had threatened this week to hit USA positions in Syria, warning that "self-restraint" over American air strikes would end if Washington crossed "red lines".
The Lebanese group released a video claiming to show an American drone tailed by an Iranian one over eastern Syria, depicting it as evidence that it could strike US targets at will. The Islamic Republic has sent scores of fighters into the country, including specialized Revolutionary Guards Corps (IRGC) militants, and has mobilized its terror proxy Hezbollah to take up arms there as well. Assad is also backed by Iran and Shi'ite militias.
The attack on the drone, Dillon said, occurred outside the established deconfliction zone, where US-led coalition troops were patrolling with their Syrian opposition counterparts.
Dillon said an assessment was underway to determine the drone's origin.
The coalition's presence in Tanf, on the Damascus-Baghdad highway, was also meant to stop Iran-backed groups from opening an overland route between Iraq and Syria, the sources say.
"As long as pro-regime forces are oriented toward coalition and partnered forces, the potential for conflict is escalated", the statement said. They were inside a "de-confliction zone", as specified by an agreement between Russian Federation and the United States to keep potentially hostile forces separated in Syria. There is now a small platoon-size element still static inside the deconfliction zone, which has not moved since coalition airstrikes destroyed a tank, two front-end loaders, another piece of construction equipment and a tactical vehicle on May 18, according to U.S. Central Command officials.
The attack Tuesday against Iranian-backed Shiite militia fighters took place near the At-Tanf Garrison on Syria's southern border.
A United States official, speaking on condition of anonymity, confirmed the strike was carried out by manned, USA aircraft.
It is the third confrontation between coalition forces and the Syrian regime near al-Tanf since mid-May.
The US military has again struck at the Syrian army in Syria. The coalition urged all parties to focus on the ISIS thread.
"Our forces are making swift advances", Zagros Qamishlo, a commander of SDF Kurdish element People's Protection Units, told VOA.
"We have repeatedly stressed: such ill-thought steps exacerbate the sufferings of Syrian civilians, and the death toll among them is growing every day".
"We have seen how clear we are about the threat that has been presented and posed to us, and we'll continue to push to have them vacate that area", Dillon said. Moscow has called on the US-led coalition to use "care" when planning airstrikes against ISIS in Syria to prevent civilian deaths, foreign ministry spokesperson Maria Zakharova was quoted by news agencies as saying.