TOKYO (Reuters) - Japanese police have arrested six men on charges of child pornography involving the abuse of at least 168 boys, Japanese media reported on Friday.

The arrests come as Japan tries to clean up its image ahead of the 2020 Tokyo Olympics. In 2014, responding to criticism that it was lax in protecting minors from sexual exploitation, Japan revised the law to ban possession of child pornography.

Media, citing a police statement, said the victims were aged 4 to 13 and more than 100,000 files of child pornography were found on the arrested men’s computers.

The arrested men were aged 20 to 66.

Some worked as volunteers at camps for elementary and middle school children, and some were elementary school teachers, media reported, adding that the suspects exchanged pornographic images directly, not over the internet, to avoid being detected.

Police said they could not immediately comment on the reports.

The number of victims of child pornography rose to a record 781 in the first half of last year, compared with 384 in the same period the previous year, according to police data.