Web search giants Google and Microsoft said on Monday they will block online searches for child abuse images.
The world's two largest search engine operators, in a rare display of unity, said as many as 100,000 search terms will now fail to produce results and trigger warnings that child abuse imagery is illegal.
The child porn crackdown announced during a Internet safety summit in London came after UK Prime Minister David Cameron in July urged Internet firms to do more to stop access to illegal images in the wake of two high-profile child sex murders in Britain.
Cameron said Britain's newly-established National Crime Agency is joining forces with the United States' FBI in a task force to track down these paedophiles and arrest them.
He described the progress to block illegal content as "significant" but said more needed to be done to track down paedophiles using the so-called "dark web" of encrypted networks that lets people anonymously share images of child abuse.
"We were told that cleaning up searches couldn't be done and shouldn't be done. We're now being told by the industry that it can be done and will be done," Cameron said in a statement after the summit at his Downing Street offices, adding that Britain would hold an international summit next year to follow-up on the agreement reached on Monday.
Both Google and Microsoft have introduced new algorithms to prevent searches for child abuse imagery.
Google executive chairman Eric Schmidt said these changes would be introduced in Britain initially and then rolled out to another 158 countries in the next six months.
Microsoft Chief Executive Steve Ballmer said deploying technology improvements to identify and eliminate Internet content that portrays child sexual abuse was a team effort.
Both companies also agreed to use their technological expertise to help in identification of abuse images and give technical support to Britain's Internet Watch Foundation and the U.S.'s National Center for Missing and Exploited Children.
Some anti-child porn campaigners, however, argued the proposals did not go far enough and called for greater funding to wipe out sharing of child porn through peer-to-peer networks.
"Every illegal image is a crime scene but law enforcement agencies do not have the resources to identify, locate and protect every victim, nor to identify, and charge every abuser," said Martyn Thomas, chairman of the Institution of Engineering and Technology IT policy panel.