TOKYO (AFP) - Japanese police have launched a probe over a controversial magazine picture of a child in a provocative pose with a naked pop singer, its publisher and reports said today.

About 670,000 copies of the popular weekly Young Magazine were pulled from stores ahead of its planned sale last weekend because of a storm over the photograph, which showed singer Tomomi Kasai with a young, apparently Caucasian or Eurasian child cupping her breasts.

The magazine's publisher Kodansha said two of its employees who handle compliance matters went voluntarily to the police "after receiving a request for a hearing over the issue".

"The child welfare section of the police department asked that the picture in question no longer be circulated," a company spokesman said, adding that police wanted all copies of the magazine taken out of circulation.

In the photograph, the blond-haired boy is shown reaching from behind to cup the breasts of 21-year-old Kasai, who until last year was a member of highly successful all-girl group AKB48, as she stares into the camera.

The photograph, on an inside page of the weekly, was released as part of a publicity drive for a book of pictures of Kasai produced by the same firm.

The mass-circulation Mainichi Shimbun newspaper today quoted one investigator as saying that police "thought this issue might turn into an international controversy".

A spokesman for the publisher earlier this week said the company accepted there was a problem with the shot, but declined to offer an opinion on whether the image fell foul of Japan's child pornography laws.

"Whether or not it is child porn, it infringes on socially accepted standards," he said.

Japan's huge publishing sector includes magazines and graphic comics containing images that may be considered obscene in other developed countries.

It is not uncommon to see people reading such material on commuter trains.