WASHINGTON (Reuters) - Authorities have arrested 14 men in a secret, members-only child pornography website that involved 251 children, mostly boys, in five countries, U.S. officials said on Tuesday.

Some of the men assumed female online personas to contact the children, who ranged in age from three to 17 years, on popular social networks, officials from the Department of Homeland Security and Immigration and Customs Enforcement said.

Eleven of the men charged with running the website, which had more than 27,000 subscribers, were from Louisiana, the officials said at a news conference. All were in custody.

The 251 victims, who have been identified and contacted by authorities, were located in 39 U.S. states. The majority were between 13 and 15 and all, but a handful, were boys.

Authorities said 23 victims were identified in the United Kingdom, Canada, New Zealand, Australia and Belgium.

"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," said Daniel Ragsdale, the ICE deputy director.

The network was identified after an item was sent through the U.S. Postal Service to a child, said James Kilpatrick, a program manager for the ICE Cyber Crime Center.

The underground website was a hidden service board on the Tor network of Darknet, investigators said, referring to a hidden online network sometimes used for illicit activities.

There are more than 300 investigations open in the United States and abroad into some of the website's subscribers, investigators said.

DHS Secretary Jeh Johnson emphasized the importance of educating youths about the dangers of Internet use.

"The fact is that many other children are still in danger," Johnson told reporters.

The men were charged with conspiracy to operate a child exploitation enterprise.

The website's main administrator, Jonathan Johnson, 27, of Abita Springs, Louisiana, faces 20 years to life in prison, said Kenneth Allen Polite, U.S. Attorney for the Eastern District of Louisiana.

(Reporting by Doina Chiacu; Editing by Bernadette Baum)

[Crime scene image via Shutterstock]