Fewer than 3,000 English-language websites produce the bulk of child pornography images, according to the first authoritative analysis of the scale of the problem, published today.

The Internet Watch Foundation, which carried out the study, says an international effort to disrupt even a few of these "persistent top level domains" would block access to hundreds of thousands of images of child sex abuse.

Peter Robbins, chief executive of the IWF, a watchdog funded by the internet industry, said the study highlighted what was a manageable number of offenders. "We hope that this revelation, and the analysis and intelligence behind the numbers will lead to a better understanding of the issue and justify the need for more international partnerships to pool resources and thinking in order to find solutions.

"A coordinated global attack on these websites could get these horrific images removed from the web and those responsible investigated."

The IWF's annual report says the scale and scope of online distribution of child sexual abuse content has been the subject of much speculation. "We have traced less than 3,000 such websites during 2007 [in the English language] hosted around the world and this figure has remained relatively static for a number of years.

"The foundation processed 34,871 reports from the public which led to 2,755 top level domains with child sexual abuse content being assessed, confirmed as potentially illegal, traced and the appropriate intelligence being disseminated accordingly."

Some IWF reports have led to prosecutions of child sex offenders.

The report says there has been a 15% fall in the number of web pages and a 10% drop in domains depicting child sexual abuse, mainly as a result of the internet industry's attempt to police itself.

It claims that this shows the problem is not increasing, despite greater global internet access, faster connection speeds and the availability of sophisticated technologies.

But the increasingly extreme nature of the content makes disturbing reading. The IWF estimates that 10% of the child victims involved in the photographs or videos appear to be under two years old. A further 33% appear to be between three and six, with 80% under 10.

Of the websites assessed, 47% depicted potentially illegal child sex abuse, including penetrative sexual activity involving children or animals.

Hardly any of the sites traced are based in Britain, with most located in the United States and Russia. The study finds that only a very small proportion of the domains identified as active last year were constantly "live", with the vast majority active for fewer than 50 days during the year. "This shows the continuing trend for such websites to 'hop' server regularly to avoid detection and removal, but also the effectiveness of efforts to make operations difficult, transient, costly and risky for offenders."

About 80% are thought to be commercial operations with the remainder made up of offenders using message boards to share abusive images.

Home Office minister Vernon Coaker said the UK internet industry's commitment to voluntarily block their customers' access to sexually abusive images of children online was leading to less content reported being confirmed as child sexual abuse. "Around 95% of those with residential broadband connections in the UK are now protected in this way, and I commend this and other positive steps taken by many companies, in conjunction with the Internet Watch Foundation, to better protect internet users, and internet services, from abuse."

Jim Gamble, chief executive of the Child Exploitation and Online Protection Centre, said its partnership with the IWF was crucial in tackling child sexual abuse material on the internet.

While the IWF had virtually eradicated this content from UK networks, the CEOP was able to focus on investigating those behind the distribution of such materials and safeguarding the victims, he said.