Hundreds of accounts, pages and groups have been banned by Facebook and Twitter over engagement in misleading political behaviour.
Facebook said it had identified and banned 652 accounts, groups and pages which were linked to Iran and to Russia for "co-ordinated inauthentic behaviour", including the sharing of political material.
The social network also confirmed it measures how trustworthy users are when they report fake news posts.
Twitter's efforts have resulted in the suspension of 284 accounts, for "co-ordinating manipulation", many of them from Iran.
It comes three weeks after Facebook last announced action against fake accounts, saying 32 had been taken down, thought to have been linked to Russia.
In a statement, Facebook said: "Some of this activity originated in Iran, and some originated in Russia.
"These were distinct campaigns and we have not identified any link or coordination between them.
"However, they used similar tactics by creating networks of accounts to mislead others about who they were and what they were doing."
Facebook said it got a tip-off about pages from a cybersecurity firm, leading them to deactivate "Liberty Free Press" which had links to Iranian state media.
The statement added: "One part of the network, 'Quest 4 Truth,' claims to be an independent Iranian media organization, but is in fact linked to Press TV, an English-language news network affiliated with Iranian state media."
Mark Zuckerberg's network has stepped up policing of Facebook since it admitted Russian agents had been able to run politically influential campaigns before the 2016 presidential election.
The new accounts may have been tied to the forthcoming midterm elections in the US.
This week, Microsoft has also reported a Russian effort to impersonate conservative US websites.
Mr Zuckerberg said: "There's a lot we don't know yet.
"You're going to see people try to abuse the services in every way possible… including now nation states."
Facebook confirmed it weighs up users' reputations when they report posts, assessing how trustworthy they are based on previous feedback they have provided.
Users who correctly report fake news will be deemed more reliable than those who falsely flag posts.
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A spokesman said: "We developed a process to protect against people indiscriminately flagging news as fake and attempting to game the system.
"The reason we do this is to make sure that our fight against misinformation is as effective as possible."
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