"The Coalition's mission is to defeat ISIS in Iraq and Syria", the US task force in charge of operations in Syria and Iraq announced on Sunday.
Coalition aircraft then stopped the pro-government forces' initial advance with a "show of force", the coalition said, adding that it does "not seek to fight the Syrian regime, Russian or pro-regime forces" but would not "hesitate to defend itself or its "partnered forces from any threat".
The Pentagon said the shoot-down came hours after Syrian government-backed forces attacked US -backed fighters, known as the Syrian Democratic Forces, in the village of Ja'Din.
A USA fighter jet shot down a Syrian jet that had dropped bombs on Coalition-partnered forces, according to a news release from the Colaition Joint Task Force.
The US-led coalition on Sunday said it downed the plane after it dropped bombs on American-backed forces fighting ISIL in northern Syria.
The last time a US pilot shot down a manned enemy aircraft was on May 4, 1999, when Lt. Col. Michael H. Geczy of the 78th Expeditionary Fighter Squadron downed a Serbian Mig-29 over Bosnia using an AIM-120 Advanced Medium-Range Air-to-Air Missile.
The Syrian Armed Forces, meanwhile, said that one of its warplanes was attacked in the Raqqa countryside, "while it was carrying out a combatant mission against ISIS terrorist organization".
The U.S. move is not the first, as U.S. forces struck Syrian military positions in the Syrian desert, where the Syrian army was advancing against IS and becoming close to the Tanf border crossing with Iraq, where United States and British military positions were installed. As the attack unfolded, the USA military used a deconfliction channel to communicate with the Syrian government to stop the skirmish, according to the Pentagon statement. US-backed forces have encircled the city of Raqqa and captured several districts from ISIL fighters.
The Syrian army said Sunday in a statement that the fighter jet crashed and its pilot is missing, Reuters reported.
Just hours earlier, the USA bombed Syrian government and allied troops inside a protected zone in that area, and marked a sharp escalation in the skirmishes between the coalition and pro-Syrian government forces there.