SAN FRANCISCO >> Facebook has purged 82 pages, accounts and groups tied to an Iranian effort to exploit its social network and Instagram service to provoke social strife in the U.S. and the U.K.

The housecleaning announced today is part of the countermeasures that Facebook put in place in an attempt to prevent abuses similar to those Russian agents used two years ago to sway public opinion ahead of the 2016 U.S. presidential election.

Facebook has even set up a “war room” at its Menlo Park, California, headquarters ahead of key elections in Brazil on Sunday and in the U.S on Nov 6. It serves as a command center for more than 20,000 workers assigned to weed out fake accounts set up to distribute false information.

In this case, that war room began to detect a pattern of “inauthentic behavior” within the cluster of pages, accounts and groups that have now been kicked off its service. All were linked to Iran, although Facebook didn’t find any ties to that country’s government, Nathaniel Gleicher, Facebook’s head of cybersecurity policy, wrote in a related blog post.

This activity was aimed at “sowing discord” by posting content focused on politically charged topics such as race relations, immigration, opposition to Trump and the polarizing Senate hearings that ended in Brett Kavanaugh’s confirmation to the U.S. Supreme.

Facebook did an even broader sweep of its service in August when it discovered 652 pages, groups, and accounts linked to Russia and Iran.

Preventing Facebook from becoming a cesspool of false information has become a top priority for CEO Mark Zuckerberg, who initially considered claims that fake news on his social network had swayed the 2016 election to be “pretty crazy .”

Facebook critics still aren’t convinced the company is doing everything it can to keep malicious activity off its service. That’s partly because sensational themes — even if they are bogus — can help keep people engaged on Facebook, helping it sell more of the ads that bring in virtually all of its profits.

In this case, some of the latest pages, accounts, and groups to be ousted were created as far back as mid-2016, Gleicher said during a conference call with reporters. And they had been posting for the past year before a manual review by Facebook determined that were malicious in nature.

“We continue to get better at finding and taking down” accounts engaged in bad behavior, Gleicher said.

It’s unclear how many people saw the content being circulated by the now-deleted accounts from Iran. About 1 million other accounts followed at least one of the offending pages. About 25,000 accounts joined at least one of the now-exiled groups and about 28,000 accounts followed at least one of the Instagram accounts that got booted.

Facebook’s social network has more than 2 billion users and Instagram has more than 1 billion.