Police in several countries have arrested scores of alleged members of an online paedophile ring and rescued 230 children in "the biggest case of its kind", Europol said.
A third of the arrests in the round-up which began three years ago were made in Britain, the policing agency said.
"Six-hundred-and-seventy suspects have been identified, 184 arrests have already been made and 230 children, the victims of these terrible crimes, have been identified and rescued from further harm," director Rob Wainwright told journalists.
"We expect these numbers to rise further," he said, adding: "This is already the biggest case of its kind we have ever seen."
The Europol operation targeted an online network that used a server based in the Netherlands and had almost 70,000 members worldwide at its height, officials said. A total 121 of the arrests were made in Britain.
Europol said the probe, dubbed Operation Rescue, started three years ago. The server involved had since been taken down and its operator appeared in a Dutch court on Tuesday.
The suspects were members of an online forum called boylover.net that promoted sex between adults and young boys, the policing agency said.
"The website attempted to operate as a discussion-only forum where people could share their sexual interest in young boys without committing any specific offences and operate below the radar," Peter Davies of Britain's Child Exploitation and Online Protection Centre told the press conference.
"Many members, however, having made contact on the site, moved on to more private channels such as e-mail to exchange and share illegal images and films of children being abused."
According to a Europol statement, computers seized from those arrested have yielded "huge quantities of child abuse images and videos".
Wainwright said this was "one of the most successful international police operations in recent years in what is probably the largest online paedophile network in the world."
The oldest of the suspects arrested over the past three years was 84. The group included at least one woman.
One suspect, arrested in Spain, worked with children at summer camps and is believed to have abused more than 100 in five years.
Most of the suspects abused children "in their closest environment, in their families or friends or neighbourhood," said Cesar Lorenzana of Spain's Guardia Civil.
According to Davies, the suspects did not share a specific profile.
"There is no particular rule about the age, there is no particular rule about the walk of life they are in. There is no particular profile of someone who is a threat to children in this way," he said.
Wainwright said investigators had a breakthrough when Europol experts cracked the Dutch-based server's sophisticated security features in 2010 to uncover "this huge network".
Europol then issued more than 4,200 intelligence reports about the activities of the network to more than 30 countries, mostly in Europe, enabling them to track down offenders and their victims.
"Our work continues and we will not rest until all of the offenders have been identified," said Wainwright, adding the number of victims was also expected to rise "maybe even significantly".
Countries involved in the probe have included Australia, Belgium, Britain, Canada, Greece, Iceland, Italy, the Netherlands, New Zealand, Poland, Romania, Spain, and the United States.