Police have questioned, on a voluntary basis, four teachers involved in the alleged bullying of a male colleague in Kobe, western Japan, according to sources close to the matter.

Reports say the accused elementary school teachers -- three males in their 30s and a female in her 40s -- repeatedly bullied the male teacher in his 20s.

They allegedly forced him to eat extremely spicy curry, put a kettle containing boiling water on his face, and performed other acts of bullying.

The teacher has been on leave since September and filed a criminal complaint with the police last month.

A lawyer for one of the teachers says the accused admits to having hit the male teacher on his shoulders but denies involvement in other acts.

Police have also interviewed the male teacher as well as other colleagues who say they witnessed the bullying.