A 15-year-old girl pled guilty to repeatedly stabbing a classmate in order to appease the fictional character known as Slender Man.

Anissa Weier admitted to plotting the sacrificial killing of her friend with an accomplice after reading horror stories about the character online.

The teenager and schoolfriend Morgan Geyser played hide and seek with Payton Leutner, before knifing her 19 times in a forest near their home in Waukesha, Wisconsin.

All three girls were 12-years-old at the time.

One of girls held down their classmate while the other stabbed her on 31 May, 2014.

The victim managed to drag herself out of the woodland and after being found by a passing cyclist, named her attackers before being taken to hospital. She underwent emergency surgery and has since recovered and returned to school.

Police found Geyser and Weier walking nearby, with a knife in one of their rucksacks. Both were charged with attempted first-degree murder.

Weier admitted the lesser charge of attempted second-degree murder as a party to a crime with use of a deadly weapon.

“I believed that if I didn’t go through with it, Slender Man would come and attack and kill myself, my friends and my family," she told Waukesha County Court. Those I cared about the most,”

An example of the Slender Man character, said to have inspired the stabbing

Slender Man started with an online post in 2009 in which a mysterious spectre was photo-shopped into everyday images of children at play.

He is typically depicted as a spidery figure in a black suit with a featureless white face and regarded alternately as a sinister force and an avenging angel.

Despite her guilty plea, Weier still faces a trial next month. It is expected to focus on whether her mental health absolves her of legal responsibility for the crime.

The teenager could face 10 years in prison if she is found guilty. She will spend three years in a mental hospital if she is found not to be legally responsible.

Geyer pleaded not guilty to attempted first-degree murder last year and is due stand trial on 16 October.

At a preliminary hearing earlier this week, Weier told the court she had not wanted to harm Miss Leutner and told Geyer she could not bring herself to stab her.

Circuit judge Michael Bohren asked the teen for her account of the attack to ensure she understood her guilty plea.

"I told [Geyer] that I couldn’t do it,” Weier said, adding that her co-defendant “asked me whether or not she should do it” when they were in the woods.

“And I just wanted it to be over with so I said, ‘Go do what you have to do,’ and Peyton was then hurt,” Weier said.

The judge asked: “How was she hurt?”

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“Morgan jumped on top of her and stabbed her repeatedly,” Weier said.

Hours after Weier’s plea, Geyser also appeared court for a preliminary hearing that focused on scheduling issues ahead of her trial.

Geyser’s lawyer, Anthony Cotton, said he and his client planned to proceed to trial. He declined comment on Weier’s plea, saying it would be inappropriate to do so.

Mr Cotton said he and his team had been holding weekly mock trials.