"Teen Mom 2" star Nathan Griffith's sister was begging for a police response after he allegedly roughed her up ... telling dispatchers he tried killing her with his bare hands.
TMZ obtained audio of the 911 call Griffith's sister placed on July 12 in Las Vegas ... and in her chat with the dispatcher, the woman says Nathan tried to strangle her before fleeing in his car.
As we first reported ... the police report says the responding officers observed visible red marks on the sister's neck and eyelids -- indicative of someone who was strangled -- and she told them Nathan grabbed her by the throat, pushed her down onto the floor and got on top of her.
Despite telling the dispatcher her brother had left, police say Nathan was still outside the home when they arrived ... yelling and denying he ever touched his sister. Ultimately, he was arrested for battery by strangulation.
We also obtained another 911 call Griffith's sister made earlier -- prior to the alleged strangulation -- and she told the dispatcher, Nathan is following her around in the home and making threats. It sounds like you can hear him in the background.
The 911 calls are alarming ... and cops also said Nathan made suicidal statements on his way to the Clark County Jail.