The Internet Watch Foundation (IWF) has reported a fourfold rise in online images depicting the most severe form of child sexual abuse. 

The IWF 2006 Annual Report (PDF) warns of a growing demand for more severe images, and claims that nearly 60 per cent of commercial child abuse websites sell images of child rape. 

Some 80 per cent of the children in abusive images are female, according to the report, and 91 per cent appear to be under 12 years old.

One of the biggest problems faced by the authorities is the effective removal of commercial sites from the web as some of the most prolific sites avoid closure by 'hopping' servers across different legal jurisdictions.

This underlines the need for unified international efforts to combat child abuse content, according to the IWF.

Another major hurdle is that some commercial child abuse websites store their images remotely, and occasionally in fragments, often on different servers around the world.

The US and Russia seem to be the main havens for hosting such sites, with 82.5 per cent of all the websites linked these countries up from 67.9 per cent in 2005.

"Sadly we have to report new trends regarding the young age of the child victims in the images we assess and the dreadful severity of abuse they are suffering," said Peter Robbins, chief executive of the IWF.

"These facts, coupled with the longevity of some commercial sites, mean that the abuse can be perpetuated for many years as the images are repeatedly viewed.

"The increase in reports processed by our 'Hotline' team is due in part to the increased awareness of our organisation, but also to the identification of a growing trend in the use of remote image storage facilities."

The IWF has claimed a 34 per cent increase in reports processed by its 'Hotline', leading to the confirmation of 10,656 URLs on 3,077 websites containing potentially illegal content.

"The UK has virtually eradicated the hosting of potentially illegal online child abuse content within its virtual borders," said Robbins.

Less than one per cent of all child abuse content has been hosted in the UK since 2003, and in 2006 the IWF provided 11 evidential statements supporting UK police enquiries and gave evidence at five UK trials.

A total of 42 reports from the IWF are still under investigation by the UK authorities.