Five teenage boys have been detained for raping and assaulting a mentally disabled 18-year-old lady in a park.

The incident took place in the western city of Mülheim, Germany, after the group reportedly lured the victim into a playground in the park.

Reports say they then dragged her into some bushes and filmed a sexual assault on their phones,

However, The Sun reports that German prosecutors admit some of them are too young to stand trial.

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Three of them are 14, the earliest age at which offenders can be prosecuted in Germany, but two are only 12, meaning they cannot be arrested or charged.

According to reports, the 18-year-old disabled was “abused in various ways”.

Residents nearby were alerted to the incident after their dogs would not stop barking.

After an hour, a 61-year-old man reportedly came out of his house after an hour and saw the woman and two suspects, who fled the scene immediately.

The man found the injured and traumatised woman on the ground and alerted police.

She was taken to hospital with unspecified injuries.

Reports have said the five teenagers are from a southern Bulgarian town and are partly related to each other.