The girl resisted him and the youth in a fit of rage chopped off her nose with a sharp weapon, the police said.
The youth, who was in a relationship with the girl, was opposed by her family.
He was arrested after the incident and a local court sent him to jail, while the girl is under treatment.
Her mother had filed a complaint with the police a month ago that the girl was being pressurised by a neighbour to marry the youth.
The police had arrested the neighbour but the youth kept harassing the girl, the police said.