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A 14-year-old girl stabbed her 11-year-old sister to death because she had been 'ungrateful', police have said.

The victim, named locally as Dora Betancourt, was found by paramedics in Chicago after her older sister called an ambulance claiming she had been attacked by an intruder.

But police say the older girl has now confessed to carrying out the killing herself.

She has been charged with murder and will appear in a juvenile court, the Chicago Tribune reports.

The mother of both girls wept as sat beside her daughter in the dock.

She was not at home at the time of the killing.

The teenager said she stabbed her younger sister because she thought she was 'ungrateful'.

The older sibling had reportedly carried out a number of chores around the house, such as making dinner, and her sister had not been thankful.

She set her alarm and woke up early to stab her sister while she was still in bed, prosecutors say.

The teenager shouted a reason for the attack with each blow, police say.

A medical examiner said there were more than 40 stab wounds, with some so deep they penetrated the child's lung.

The girl will appear again in court on January 31.