Japanese girl band star Tomomi Kasai at centre of 'child porn' investigation after magazine used picture of her with boy touching her breasts

Police in Tokyo are interviewing a magazine publisher over a photograph showing a young female pop star in an 'inappropriate pose' with a boy.

The photograph, showing AKB48 singer Tomomi Kasai, 21, naked with a blond child cupping her breasts from behind, was to be published in Shukan Young Magazine.

Publisher Kodansha was planning to run the photograph, which came from a forthcoming book of photographs of the singer, in its weekly manga (or comic-style) magazine earlier this month.

But that edition didn't make it to the newsstands, and detectives were called in after conces were raised that the picture might infringe even Japan's notoriously lax child poography laws.

Tomomi Kasai is a huge star in Japan, where she has been a singer since the age of 14 and is best known for being a part of the phenomenal, 91-strong girl group AKB48.

The group - the world's largest - is one of the highest-eaing musical acts in the world and recruits new members through Pop Idol-style auditions.  All the girls must be well-behaved, and they perform in a theatre every day, with tickets only available through a heavily-subscribed lottery.

Initially Kodansha said the delay in getting the magazine out was due to it containing an 'inappropriate expression' but police said they needed to investigate further and called staff in to be interviewed.

Kodansha pulled the photograph and postponed the sale of the magazine from January 12 to January 21.  They also took it out of their planned collection of photographs of the singer.

Investigators, who say their first job is to discover if the photograph is real or not, say they will take into consideration the fact that the edition featuring the picture was scrapped before it was published.

The Japanese Law Banning Child Prostitution and Child Poography says that any photo that depicts a child touching the breasts or sexual organs of another individual and which could sexually arouse or stimulate a viewer is defined as child poography, according to asahi.com.

Japanese phenomenon: Tomomi Kasai (fourth from left, back row) is pictured with some of her group AKB48

The website quoted Toru Okumura, a lawyer who has worked on child poography cases, saying: 'The Osaka High Court...last July found that if anyone, even a small number of people, became sexually aroused, that would fulfill (the condition in the child poography definition).'

He added: 'Regardless of whether or not a large number of people would become sexually aroused by a photo of a child touching someone else's sexual organs, there is the possibility of the photo being considered poography.'

Japanese website tokyoreporter.com said that the country's child poography laws stipulated a maximum of five years in prison and a fine of five million yen.

It quoted the investigating team as saying: 'In comparison to Japan, penalties in Europe for using a young boy in child poography are more severe.

'We are taking into account that this could be a problem at an inteational level.'

Kodansha issued an apology, saying: 'In future we will endeavour to do our best to respect the freedom of speech of an author, writer, cartoonist or photographer.

'We are committed to working with more compliance measures in place as we continue to engage in our publishing activities.'

Kasai joined AKB48 in 2006 but announced last month that she was planning to 'graduate' from the group.

The photograph collection, which will be her first solo book, is entitled 'Tomo no koto, suki?' (Do you like Tomo?) and is expected to be published without the offending image next month.