A Japanese man and his son face human trafficking and child abuse charges involving the mistreatment of 13 compatriots on a small island in the southern Philippines, police said Wednesday.

They said Hajime Kawauchi, 61, and his son, Yuya, 34, have been detained since May 3, along with a Filipina woman. They were arrested on suspicion of taking in the Japanese individuals, aged 13 through 20, as students of their English and karate training center without having obtained necessary permits and forcing them to perform tasks outside of the original purpose of their stay in the country.

"Upon verification by the Bureau of Immigration, it was found out that those students had no permit to study in the country. It was also found out that some of the kids were maltreated and subjected to forced labor," Chief Inspector Milgrace Driz, spokesman for the police in the region, said by phone.