Through a network of fake news websites and fraudulent social media personas spread across Facebook, Instagram, Twitter, Google Plus and YouTube, the Iranian-linked campaign pushed narratives in line with the country's interests.
The campaign was aimed at users in the United States, Britain, Latin America and Middle East up through this month, according to an analysis by the cybersecurity company FireEye Inc (FEYE.O), which first spotted the behavior.
Russia has been linked to similar online influence campaigns, including an effort to sow political divisions among U.S. voters, but FireEye said its findings showed that the same tactics are now being used for different aims.
The firm said the Iranian activity included "anti-Saudi, anti-Israeli, and pro-Palestinian themes" and advocacy of policies favorable to Iran such as the U.S.-Iran nuclear deal.
Microsoft on Monday said that hackers linked to the Russian government sought to steal email login credentials from U.S. politicians and think tanks.
FireEye said the Iranian activity did not appear "dedicated" to influencing the upcoming election, though some of the posts aimed at U.S. users did adopt "left-leaning identities" and took stances against President Donald Trump.
That activity "could suggest a more active attempt to influence domestic U.S. political discourse" is forthcoming, Foster said, but "we just haven't seen that yet."
FireEye said the U.S.-focused activity ramped up last year, just months after Trump took office, with websites and social media accounts posting memes and articles, some of which were apparently copied from legitimate U.S. and Iranian news outlets.
In some cases, the domains for the fake websites like 'US Journal' and 'Liberty Free Press' were originally registered years before the 2016 election, in 2014 and 2013, but most remained inactive until last year, FireEye said.
Arabic-language, Middle East-focused websites appear to be part of the same campaign, the company added.
Facebook said it removed 254 pages and 392 accounts across its flagship platform as well as its Instagram service. Some of the accounts had events and groups associated with them.
The accounts spent about $12,000 to advertise through Facebook and Instagram using a variety of currencies, Facebook said. The company said it had notified the U.S. Treasury and State departments of the purchases, which may potentially violate sanctions.