(TMZ) -- XXXTentacion says he got jumped by Migos in L.A. -- and even posted video of what appears to be one of its members walking away from the fight ... plus Cardi B's photo.

X went on an Instagram rant Monday claiming he'd just been jumped by the rap trio, adding they allegedly pulled a gun on him during the scuffle.

He then deleted almost every post from his IG page and left only one -- a video of what he claims is Takeoff walking away from the brawl.

Unclear what set off the alleged jumping, but whatever the beef is ... it's probably only going to get worse now that X got Cardi involved. 

**WARNING: Explicit language**

Photo: Getty Images