Facebook says it has deleted accounts originating in Iran that featured posts on politically divisive topics and attracted more than 1 million followers in Britain and the United States.
The social network on October 26 said it deleted 82 accounts and pages on Facebook and Instagram that were "fake" and posted on divisive issues such as race, immigration, and U.S. President Donald Trump -- all of which it said were aimed at "sowing discord" ahead of U.S. congressional elections on November 6.
The deleted accounts represented themselves as being American or British and mostly targeted U.S. liberals, according to the Atlantic Council's Digital Forensic Research Lab, a think tank that works with Facebook to study propaganda online.
Facebook said the deleted accounts had attracted more than 1 million followers. It said their posts had been amplified through less than $100 in advertising on Facebook and Instagram in the last year.
Facebook said it spotted coordinated activity between the accounts only a week ago, and moved quickly to stop it, given the looming U.S. elections.
"It looks like the intention was to embed in highly active and engaged communities by posting inflammatory content, and then insert messaging on Saudi [Arabia] and Israel which amplified the Iranian government's narrative," said Ben Nimmo, an information defense fellow with the Digital Forensic Research Lab.
Saudi Arabia and Israel are both avowed enemies of Iran. While the accounts originated in Iran, Facebook said it was unclear if they were linked to the Tehran government.
The social-media giant, the world's largest with 3 billion followers worldwide, said it shared information about the accounts with researchers, other technology companies, and the British and U.S. governments.
"These accounts masqueraded primarily as American liberals, posting only small amounts of anti-Saudi and anti-Israeli content interspersed within large volumes of divisive political content such as race relations, police brutality, and U.S. President Donald Trump," the Atlantic Council said in an online post.
"This evolution of tactics from previous, more blatant pro-Iranian messaging suggests the operation had learned from earlier take-downs," it said.
In August, Facebook, along with Twitter and Google, removed hundreds of accounts linked to Iran.
Iran did not immediately respond to the latest accusations. Tehran has previously denied allegations that it uses social media for disinformation campaigns.
Facebook's head of cybersecurity policy, Nathaniel Gleicher, told reporters on a conference call that the latest operation uncovered by Facebook was more sophisticated than past incidents in ways that made it difficult to identify.
Although most of accounts and pages had existed only since earlier this year, they attracted more followers than the accounts removed in August, some of which dated back to 2013, he said.
The previously suspended Iranian accounts and pages garnered roughly 983,000 followers before being removed, he said.
Social-media companies have increasingly targeted foreign interference on their platforms following criticism that they did not do enough to detect, halt, and disclose Russian efforts to use their platforms to influence the outcome of the 2016 U.S. presidential race.
Facebook says it has set up a "war room" at its Menlo Park, California, headquarters ahead of the U.S. elections, as well as a presidential election in Brazil on October 28. The war room is staffed with more than 20,000 workers assigned to weed out fake accounts set up to distribute false information.