Facebook has removed 82 Pages, Groups and accounts for what it calls "coordinated inauthentic behaviour" that originated in Iran and targeted people in the US and Britain.
"While we have found no ties to the Iranian government, we can't say for sure who is responsible," Nathaniel Gleicher, Head of Cybersecurity Policy at Facebook said in a statement on Friday.
The people behind these Pages and accounts represented themselves as US citizens, or in a few cases UK citizens -- and they posted about politically charged topics such as race relations, opposition to the US President, and immigration on Facebook and Instagram.
Facebook said its threat intelligence team first detected this activity one week ago and conducted an internal investigation.
"Despite attempts to hide their true identities, a manual review of these accounts linked their activity to Iran," Gleicher said.
The activities on Facebook were revealed just weeks before the midterm election in the US and while a heated Brexit debate continues in Britain.
"Given the elections, we took action as soon as we'd completed our initial investigation and shared the information with US and UK government officials, US law enforcement, Congress, other technology companies and the Atlantic Council's Digital Forensic Research Lab," Gleicher said.
Facebook said about 1.02 million accounts followed at least one of these Pages, about 25,000 accounts joined at least one of these Groups, and more than 28,000 accounts followed at least one of these Instagram accounts.
This is not the first time Facebook has removed Pages and accounts linked to Iran. In August, the social network removed 600 Pages and accounts originating from Russia and Iran for engaging in "inauthentic behaviour".