Facebook said it has uncovered "sophisticated" efforts, possibly linked to Russian Federation, to influence USA politics on its platforms.
"We're still in the very early stages of our investigation and don't have all the facts - including who may be behind this", the company said in a statement.
In total the accounts had 9,500 posts, all but one of them on Facebook, the other on Instagram.
A Facebook event co-organized by, Resisters, one of the now-banned Pages. The accounts had about 150 ads for approximately $11,000 on Facebook and Instagram.
Why can't Facebook be sure who is responsible? Based on the information Facebook released, this particular group of fake pages was targeting people on the left.
They also used third parties to publish paid advertisements on Facebook, in violation of the social media firm's policies banning foreign entities from buying USA political ads.
The company's announcement comes after it has faced congressional questioning this year about whether it has marginalized conservative voices or allowed nutty sites to exist, and in the wake of last week's huge market drop in the share price following Facebook's announcement the pace of new accounts opening had slackened.
They also created 30 fake "events", with one event - which Facebook did not name - having 4,700 people saying they were interested in going, and 1,400 users saying they would attend. The pages repeated progressive talking points and set up real-world events aimed at rallying genuine left-wing activists.
One of the fake account's posts.
Sandberg said on the call that Facebook wanted to disclose its findings on the coordinated campaign because of the timing of the event. In another, the "Resisters" page created a Facebook Event post for an alleged protest that would be held in Washington next month to clash with an already scheduled rally to "Unite the Right". The company also said it had reported the network to law enforcement and to Congress.
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Facebook said it will work with law enforcement to understand where these pages came from and will continue to monitor its platform.
How have United States politicians reacted?
Facebook said it chose to share the information, despite not having all the facts, because there was a "connection" between the pages in question and a number of protests that were planned for Washington, DC next week.
"Foreign influence actors remain readily capable of manipulating raw emotion and societal divisions to prey on unsuspecting Americans who use these same social media tools for legitimate political expression, organisation, and advocacy". Mark Warner (D-VA), who sits on the Senate Intelligence Committee, commended Facebook for its swift action.
Facebook said it had briefed U.S. law enforcement agencies, Congress and other tech companies about its findings.
What happened with the 2016 elections?
"Today's announcement from Facebook demonstrates what we've long feared: that malicious foreign actors bearing the hallmarks of previously-identified Russian influence campaigns continue to abuse and weaponize social media platforms to influence the USA electorate", he said.
But he has since apologised for being so dismissive.
The network is the most extensive effort to interfere in American politics that Facebook has found and made public ahead of November's midterm elections.
The activity had "similar qualities" to what the Russian-backed Internet Research Agency employed in advance of the 2016 elections, according to multiple sources who were briefed on the matter but not authorized to speak publicly.
Two weeks ago, he caused an worldwide firestorm when he stood alongside Russian President Vladimir Putin and cast doubt on assertions that Russia tried to sabotage the vote.