Facebook, along with Twitter and Alphabet, in August removed hundreds of accounts tied to an Iranian propaganda effort.
Facebook said on Friday it had discovered Iranian disinformation activity on the social network a week ago and removed more than 80 inauthentic accounts, groups and pages spreading "politically charged" posts targeted at U.S. and U.K. citizens.
"As soon as we detected this activity, the teams in our elections war room worked quickly to investigate and remove these bad actors," Nathaniel Gleicher, Facebook's head of cybersecurity policy, wrote in a blog post. "Finding and removing abuse is a constant challenge. Our adversaries are smart and well funded, and as we improve their tactics change."
Described as "coordinated inauthentic behavior," the activity focused on spreading political messages, and used fake identities to deceive users.
A source directly familiar with the situation who was not authorized to speak publicly said what Facebook uncovered from Iran was "straight out of the Russian playbook" to drive online conversation in the U.S., in this case to "stoke the left."
The source added that this is a marked shift by the Iranians away from the traditional anti-Saudi Arabia and anti-Israel propaganda to the Russian model used in the lead up to the 2016 U.S. election. The ultimate goal is to build an audience online and spur Americans to argue with each other, the source said.
Facebook said it found that more than one million people followed at least one group spanning across both Facebook and Instagram.
"Page administrators and account owners typically represented themselves as US citizens, or in a few cases, U.K. citizens," and generated posts that featured "politically charged topics such as race relations, opposition to the President, and immigration," Gleicher wrote.
Friday's announcement was the second from Facebook regarding Iran-linked misinformation efforts on its social network. In August, Facebook and Twitter removed hundreds of "accounts tied to an alleged Iranian propaganda operation" that also featured posts attempting to cultivate political discourse.
The first instance Facebook cited in the most recent set of Iranian activity dates back to June 2016.
Facebook has now has 20,000 employees dedicated to policing the site and detecting fake accounts on the platform, according to the blog post.
While the company discovered the activity "originated in Iran," they "have found no ties to the Iranian government."