'Expendables 2' -- Stuntman's Family Sues Over Deadly Explosion

The family of a stuntman who was killed during an explosion on the set of "​The Expendables 2" is suing producers ... claiming they failed to take proper safety precautions during a stunt-gone-wrong in Bulgaria.

According to the lawsuit, Kun Liu was shooting an action scene that took place on a rubber boat near the Ognyanovo Reservoir on October 27, 2011. The scene involved the use of high powered explosives and other "ultra-hazardous activities."

But something went horribly wrong ... and according to the suit, 26-year-old Liu was killed during the filming of the scene.

Liu's parents blame the production company, Millennium Films, and the stunt coordinator, Chad Stahelski ... and now they're suing both parties for wrongful death.

Liu's family believes they should be compensated for funeral expenses ... and for the loss of their son's "society, love, comfort, attention, services and support."