Police will step up cooperation with an association of Internet service providers next month to crack down on the distribution of child pornography.

The move by the National Police Agency and 23 ISPs comes as Japan has been accused of being too soft on child pornography.

The law against child porn bans intentional distribution, but it does not prohibit possession of pornographic images of children or unintentional distribution through file-sharing applications.

In the case of the software called Share, downloaded files can be automatically shared on the Internet even if users do not intend to share them.

When a transmission of child porn is detected on the Internet, the police will inform the association of the sender's IP address and the file names. The industry body will send an email to whoever sent the images, warning against the transmissions and urging them to delete the files.

Those who fail to comply will be regarded as intentional distributors.

"Controls until now could not sufficiently prevent" the spread of child pornography, a NPA official said.

A preliminary program initiated in September 2012 by the Shiga Prefectural Police and a service provider detected about 150 files containing child porn. Distributors of those files all took steps to prevent file-sharing after being warned, according to the Shiga police.