As Vietnam war veteran John Rambo, Sylvester Stallone has caused a lot of destruction, but none of the on-screen brutality can compare to the very real one he witnessed while shooting John Rambo, the fourth installment of the series, along the precarious border of Thailand and Burma.

“[There’s] a full-scale genocide that’s been going on with a cloud of mystery over it because the Burmese are so rich,” Sly tells Entertainment Tonight in an interview to air Friday. “It’s the most brutal regime in the world and the most secretive. It has an oppressive regime that keep[s] all [riches] for themselves. Everyone is forced into drugs or prostitution or slavery."

Dismemberment and cannibalism were prevalent, the actor says, and the film crew itself wasn’t exempt from these deadly situations. “We were on the Salween River and we were told to get out because we were going to be shot. All the people you see in the movie are real Burmese refugees. When it was announced that (a Burmese man) would be playing the pirate in the movie, his parents were jailed and his niece was savagely raped by the army."

But through all the violence, they managed to complete the action flick, which will hit theaters on Jan. 25, 2008, and the 61-year-old assures “it’s the best of all the Rambos," if only for its social message.

"It was a tough shoot, but I like doing it at my age. As you get older you have something to prove, so you push yourself. I wanted to do one more but I also wanted to touch on something that has been going on for 60 years. It’s the longest civil war in the world. The most important thing is you provide entertainment but you also put a light on this savage existence that the people in Burma have to live."

For the complete interview, check out ET on Friday.

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