A 14-year-old boy accused of repeatedly stabbing a female classmate during a school assembly attacked her when she refused his romantic advances, police say.

The teen girl told investigators the boy had tried to start a romantic relationship with her, but she told him she liked him “only as a friend”.

The boy then reportedly stabbed the girl nine to 11 times with a 10cm folding knife that had a serrated edge, Fox News reported.

View photos A 14-year-old Oklahoma boy accused of repeatedly stabbing a female classmate attacked her when she refused his romantic advances, police say. Source: KOCO/ABC5 More

Investigators had earlier been tight-lipped about a possible motive behind the August 16 stabbing at Luther High School, Oklahoma, US. The attack happened as students gathered on the first day of school.

A teacher was able to subdue the boy and take the knife from him, while other teachers gave the girl CPR as they waited for first responders to arrive.

Police Chief David Randall confirmed the girl had been released from hospital.

View photos The 14-year-old victim is transported to hospital by helicopter after being stabbed 9 to 11 times. Source: KOCO/ABC5 More

The boy remains in the Oklahoma County Juvenile Detention Center and faces charges of assault and battery with a dangerous weapon.

Chief Randall told NBC News he was struck by the boy’s “nonchalant attitude” about what he had done, as the teen showed “no remorse whatsoever.”

Luther Public Schools shared a statement on their website shortly after the incident, saying: “There was an incident at the High School Assembly this morning at the Auditorium.

“The situation is under control, the students at the high school are safe.”