Facebook has uncovered and removed dozens of pages, accounts and groups linked to Iran that the firm says coordinated "inauthentic behaviour", targeting people in the US and UK.
The affected posts focused on divisive topics such as race relations, opposition to President Donald Trump and immigration, it said.
The social network revealed that it uncovered the activity a week ago.
"We can't say for sure who is responsible," it said in a blog post.
It added that it had so far found no ties to the Iranian government but that its investigation was ongoing.
The company said it had identified 82 pages, groups and accounts that were coordinating inauthentic behaviour on Facebook and Instagram in violation of the platform's policies.
Only two advertisements were connected to the effort, it said.
While the earliest signs of the activity date to June 2016, Facebook said much of the activity occurred over the last year.
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