NOORDWIJK, Netherlands - Police in Sweden have broken a major child pornography operation after a lengthy joint effort involving INTERPOL and Norwegian investigators, INTERPOL officials announced on Thursday.

A series of police raids on residences in Stockholm on May 13 led to the arrest of a man suspected of producing the most sought after series of child pornography images available to collectors of such material, INTERPOL officer Hamish McCulloch said during INTERPOL's annual European Conference. Social workers and crisis counselors have already interviewed 15 children thought to be victims and this number could rise to 40, he said.

The pornographers produced some images to order for collectors.

'This was a very complex case and the production of these pornographic images, a series often using the same children, had been going on for more than five years,' Mr McCulloch said. 'The investigation, which used INTERPOL's child pornography database and sophisticated image analysis, allowed Norwegian police, and then police in Sweden, to break up the operation and make the key arrest.'

INTERPOL in 2001 provided Norwegian police with approximately 1,500 images from its extensive image child pornography database and Norway then assigned officers to follow up on INTERPOL's analysis. Technical examination of such things as vegetation and rock formations in outdoor scenes allowed investigators to narrow down their search for the region where the images were being produced.

A breakthrough after analysis of computer and Internet data led to the Stockholm raids this week.

'This is an excellent example of how INTERPOL information and analysis enhances international police cooperation and leads to arrests,' said Anders Persson, a Swedish police officer seconded to work at INTERPOL's General Secretariat in Lyon.

INTERPOL has been stepping up its investigation and analysis of child pornography images since 1997. Its database of some 150,000 photographs allows police around the world to compare images and make important links between locations, images and photographic styles.