The Fighter Jet was shot down by US Forces recently and you can read about that here
An American fighter jet shot down a Syrian government bomber in the eastern part of the country on Sunday, in one of the clearest signs yet of an open conflict between the United States and the regime of Syrian President Bashar Assad.
The downing of the Syrian plane raises the possibility of future fighting between pro-Assad forces and U.S. forces that are deployed in Syria in support of Syrian militias battling the Islamic State.
During the first six years of the Syrian crisis, the United States supported rebel groups fighting Assad, but avoided direct conflict with his forces. That changed on April 6 when U.S. President Donald Trump ordered a cruise missile attack on a Syrian air base in response to a chemical attack that killed more than 70 people including civilians. Now, it has engaged in air-to-air combat in Syria for the very first time.
Russia, whose armed forces offer critical support to the Assad government, threatened retaliation. In a statement, the Russian defense ministry said it would regard any U.S. coalition aircraft detected west of the Euphrates river in Syria as legitimate targets. The ministry called the downing of the Syrian jet “a cynical violation of Syria’s sovereignty.” Moscow also shut down the “deconfliction” channel designed to prevent midair contact between Russian and American warplanes in the skies over Syria.