Bosnian police secure the area after a shooting at an elementary school in the northeastern city of Lukavac on Wednesday. AFP

The teacher, a 38-year-old man who also served as the assistant headmaster in Lukavac Elementary School in the northeastern town, sustained serious wounds and was undergoing surgery, police said in a statement. The assailant was detained after the shooting in which no students were injured, the statement added.

Police released no information about the shooter’s motive, but local officials confirmed the boy was expelled from the school earlier this year for unruly behaviour. A local politician in Lukavac, Dino Osmanovic, claimed the boy had previously threatened to take revenge for the disciplinary action.

Osmanovic said he notified the police of the danger in late May, but was told they had taken "necessary measures, that everything was under control and that they cannot share more information about the case because it involves a juvenile.”

The shooting comes on the heels of two mass murders in neighbouring Serbia where, in early May, a 13-year-old boy took his father’s gun to school in Belgrade and opened fire on his fellow students.

The shooting claimed the lives of nine students and a school guard. A day later, a 20-year-old used an automatic weapon to randomly target people in two villages south of Belgrade, killing eight people and wounding 14.