A teacher at a Tokyo school has been arrested for making a group of boys undress at knifepoint and stealing their underpants.

A group of eight boys, aged 12 to 13, were playing in school grounds earlier this month when the 26-year-old man, who teaches at a different school, approached them, Kyodo news agency said.

Two of the boys ran away but he made the other six take off their trousers and underpants, Kyodo quoted local police as saying. The knife touched one boy, causing minor injuries, Kyodo reported.

The teacher is also suspected of taking a mobile phone from one of the boys and making nuisance calls to his home afterwards, Kyodo reported.

The principal of the school where he taught was shown on TV saying he was a dedicated teacher.

Tokyo police declined to comment on the case.