(CNN) -- Investigators have busted an international pedophile ring that charged people money to watch live online broadcasts of Filipino children being sexually abused, authorities said.
Under way since 2012, the operation has resulted in the arrest of 29 people, 11 of them from the group in the Philippines that facilitated the abuse, Britain's National Crime Agency (NCA) said in a statement Wednesday.
Some of the people who arranged for the abuse, which was filmed on webcams, were from the children's own families, it said.
Fifteen children between the ages of 6 and 15 have been rescued in the Philippines, the British agency said.
The investigation was a joint effort between the NCA, the Australian Federal Police and U.S. Immigration and Customs Enforcement.
The operation began after British police found "indecent videos" on computers at the home of a registered sex offender.
The ensuing investigation eventually uncovered the abuse being carried out in the Philippines and people in other countries who were involved in the pedophile ring, the NCA said.
Seventeen arrests were made in Britain, the agency said, resulting in five convictions.
"This investigation has identified some extremely dangerous child sexual offenders who believed paying for children to be abused to order was something they could get away with," said Andy Baker, deputy director of the NCA's Child Exploitation and Online Protection command.
"Being thousands of miles away makes no difference to their guilt. In my mind, they are just as responsible for the abuse of these children as the contact abusers overseas," he said.
An Internet scourge
Children's rights advocates say that cyber-sex crimes can be difficult to track down because the private nature of the technology allows crimes to take place in a venue that law enforcement can't easily access, making it harder to gather evidence against perpetrators.
Conditions in the Philippines -- such as widespread poverty, an established sex trade, a predominantly English-speaking, technologically-literate population and widespread Internet access -- have made the country vulnerable to such abuse.
"A vast and comparatively wealthy overseas customer base has led to organized crime groups exploiting children for financial gain," the NCA said.
The British agency cited online conversations in which two of the men convicted under the investigation, Timothy Ford and Thomas Owen, discussed ways to travel to the Philippines to engage in direct abuse of children.
In one webchat, Ford, who uses a wheelchair, proposed that Owen could behave as his carer as way to avoid being caught, the agency said.
Ford was sentenced to eight and half years in prison in March; Owen was sentenced to seven years in prison in July.
The NCA said more than 37,500 pounds ($61,000) had been paid through the crime network in exchange for viewing the abuse of children.
Three other separate investigations are under way into the live-streaming of child sexual abuse and have identified 733 suspects worldwide, the agency said.
CNN's Pierre Meilhan contributed to this report.