Facebook says it has removed 652 accounts and web pages linked to Russia and Iran for spreading political misinformation ahead of the November U.S. congressional elections.
The social network said late on August 21 that it had removed the accounts from Facebook and Instagram because they engaged in "coordinated inauthentic behavior" that included the sharing of misleading political material.
Twitter also announced late on August 21 that it had taken down about 300 accounts promoting Iranian propaganda with anti-Saudi, anti-Israeli, and pro-Palestinian themes, Reuters reported. Twitter said the "coordinated manipulation" on its platform started last year.
Facebook has significantly stepped up policing of its widely used network since last year, when it acknowledged that Russian agents successfully ran political influence operations on Facebook aimed at swaying the 2016 U.S. presidential election.
The social network said it had informed the U.S. and U.K. governments about its actions as well as the U.S. Treasury and State Department because of U.S. sanctions against Iran.
"We ban this type of behavior because authenticity matters, and people need to trust what they see on Facebook," CEO Mark Zuckerberg told reporters on a conference call, but he added that "there's a lot we don't know yet" about the players behind the accounts.
In Moscow, Kremlin spokesman Dmitry Peskov said on August 22 that the Russian government did not understand why Facebook decided to take down the accounts.
"We've seen these reports," Peskov said. "We don't understand what Russian intelligence services have to do with this, what gave Facebook this idea, and why they thought that this has to do with us."
There was no immediate reaction from the Iranian government about Facebook's allegations and deletion of the pages.
Facebook said its latest actions stemmed from four investigations -- three involving Iran, and one involving Russia.
The first involved a group called "Liberty Front Press" that set up multiple accounts on Facebook and Instagram that were followed by 155,000 other accounts. The group was linked to Iranian state media based on website registrations, IP addresses, and administrator accounts, Facebook said.
The first accounts were created in 2013 and posted political content about the Middle East, the United Kingdom, and the United States, Facebook said.
The second group also had multiple accounts and 15,000 followers. The group was linked to Liberty Front Press and attempted to hack people's accounts to spread malware. Facebook said it disrupted those attempts.
A third group which also operated out of Iran had as many as 813,000 followers, and also shared political content about the Middle East, the United Kingdom, and the United States.
In all, the Iranian-linked groups spent some $12,000 in advertising and hosted 28 different events, Facebook said.
A fourth group that attempted to influence politics on issues involving Syria and Ukraine was linked to sources that Facebook said the U.S. government has linked to Russian military intelligence.
"While these are some of the same bad actors we removed for cybersecurity attacks before the 2016 U.S. election, this more recent activity focused on politics in Syria and Ukraine," said Facebook's head of cybersecurity policy, Nathaniel Gleicher.
The accounts were associated with Inside Syria Media Center, which the Atlantic Council and other organizations have identified as covertly spreading pro-Russian and pro-Assad content.
"We're working closely with U.S. law enforcement on this investigation," Facebook said in a blog post.