The Epoch Media Group denied in an email sent to The New York Times that it was linked to the network targeted by Facebook, and said that Facebook had not contacted the company before publishing its conclusions.

The people behind the network used artificial intelligence to generate profile pictures, Facebook said. They relied on a type of artificial intelligence called generative adversarial networks. These networks can, through a process called machine learning, teach themselves to create realistic images of faces, even though they do not belong to a real person.

Nathaniel Gleicher, Facebook’s head of security policy, said in an interview that “using A.I.-generated photos for profiles” has been talked about for several months, but for Facebook, this is “the first time we’ve seen a systemic use of this by actors or a group of actors to make accounts look more authentic.”

He added that this A.I. technique did not actually make it harder for the company’s automated systems to detect the fakes, because the systems focus on patterns of behavior among accounts.

Ben Nimmo, director of investigations at Graphika, said that “we need more research into A.I.-generated imagery like this, but it takes a lot more to hide a fake network than just the profile pictures.”

Facebook said the accounts masked their activities by using a combination of fake and authentic American accounts to manage pages and groups on the platforms. The coordinated, inauthentic activity, Facebook said, revolved around the media outlet The BL — short for “The Beauty of Life” — which the fact-checking outlet Snopes said in November was “building a fake empire on Facebook and getting away with it.”