They say that 14 men running a secret, members-only child porn website have been arrested.
About 250 children – mostly boys from the US – appeared on the site.
The website had more than 27,000 subscribers, many of whom have been charged in individual cases.
“Never before in the history of this agency have we identified and located this many minor victims in the course of a single child exploitation investigation,” Immigration and Customs Enforcement (Ice) Deputy Director Daniel Ragsdale told Reuters news agency.
Ice worked with Homeland Security officials and other agencies to break up the ring, which ran a website to share videos of boys enticed from social networks into providing sexually explicit material – sometimes by men posing as women.
Ages of the children ranged in age from three to 17 years, officials said, and came from 39 US states. Twenty-three of the 251 victims were identified in Britain, Canada, New Zealand, Australia and Belgium.
Among the suspects arrested was Jonathan Johnson, 27, the alleged administrator of the child porn website, which operated out of the southern US state of Louisiana.
If convicted, he faces 20 years to life in prison, officials say.
“These indictments represent a strong co-ordinated strike… Against child pornography and those who allegedly seek to harm our most vulnerable citizens, our young children,” Louisiana Eastern District Attorney Kenneth Allen Polite told the AFP news agency.
Police say that the illegal website operated on a hidden service board on the Tor network from about June 2012 until June 2013, when Mr Johnson was arrested.
The Tor network is set up to conceal a user’s location, allowing him or her to maintain online anonymity.
But the porn ring was broken when an item was sent through the US Postal Service to a child, Ice Cyber Crime Centre Programme Manager James Kilpatrick told Reuters. That development led the authorities to Mr Johnson.
The 14 men arrested have been charged with conspiracy to operate a child exploitation enterprise.
At the time it was dismantled, the illegal website contained more than 2,000 shared webcam-captured videos of mostly juvenile boys, officials say.
Ice officials warn that a growing number of children are being enticed into sharing sexually explicit material online.
“We cannot arrest our way out of this problem: education is the key to prevention,” Mr Ragsdale said.