Facebook announced Wednesday morning that it had removed a small network of fake social media accounts it said were run from Iran and were posting about US politics. Twitter also said it removed accounts from Iran, but said its investigations were ongoing and provided few details.

The takedowns are the latest in a series of moves by Silicon Valley to crack down on covert information campaigns run from Iran that use fake accounts and pose as Americans.

Last month CNN exclusively reported how “American Herald Tribune,” a purportedly independent online media outlet, originated in Iran.

In a company post about Wednesday’s takedown, Nathaniel Gleicher, Facebook’s head of security policy, wrote that the Iranian accounts “shared posts about political news and geopolitics including topics like the US elections, Christianity, US-Iran relations, US immigration policy, criticism of US policies in the Middle East, public figures, as well as video interviews with academics, public figures, and columnists on issues related to Iran and US elections.”

Examples of the purportedly Iranian posts shared by Facebook include one criticizing former Trump national security adviser John Bolton.

FireEye, a cybersecurity firm that had been tracking accounts associated with the network Facebook removed, said some had posed as journalists on social media. Other accounts, the company said, had posed as US liberals and shared content “broadly in line with that proclaimed political leaning, as well as material more directly in line with Iranian political interests.”

FireEye said it had seen this activity on Twitter also. A Twitter spokesperson confirmed to CNN on Wednesday that it had removed “a small number of accounts originating in Iran.”

Facebook removed six Facebook accounts and five Instagram accounts it said were part of the network. Only 60 people followed one or more of the Instagram accounts, Facebook said.

Facebook also announced Wednesday that it had taken down a network of accounts targeting Ukraine that the company said was linked to Russian military intelligence.

Ben Nimmo, director of investigations at Graphika, a social media analysis company, analyzed the Russian accounts Facebook removed and said the people behind the accounts had used personas to post articles on blogs. The same tactic was used by Russian military intelligence to run articles on real American websites in 2016, as CNN previously reported.

Facebook also removed a network of accounts targeting people in Myanamar that it said was linked to two telecom companies.