The girl was a student at the school where the teacher worked but police said they have not yet established a personal relationship between the pair.
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The girl was discovered by her grandmother, an official at the Daejeon Metropolitan Office of Education said during a media briefing on Tuesday.
She was found with stab wounds in the neck and face, a local fire department official told Reuters on Monday, and later died in hospital.
The female teacher, reported to be in her 40s, has been treated for self-inflicted wounds in hospital following the attack in the city of Daejeon on Monday.
