"On Sunday evening, United States law enforcement contacted us about online activity that they recently discovered and which they believe may be linked to foreign entities", Nathaniel Gleicher, the company's head of cybersecurity, said in a statement.
In a statement published the night before polls opened, the company said it had been contacted by the police about suspicious behaviour believed to be linked to foreign entities. "We had already blocked most of these accounts yesterday, and have now blocked the rest", Facebook added.
According to the statement, nearly all the Facebook Pages, which were associated with the blocked accounts, were in either French or Russian.
Researcher Andre Souza works in Facebook's "War Room" - the nerve center for the fight against misinformation and manipulation of the largest social network by foreign actors trying to influence elections in the USA and elsewhere.
The Instagram accounts were mostly in English and were focused either on celebrities or political debate.
It was the USA law enforcement that warned Facebook about these accounts.
Last month alone, Facebook removed 800 pages and accounts deemed to be spreading misinformation to influence public opinion on both the right and left.
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Reuters was first to report that the Pentagon had balked at the initial request from the Department of Homeland Security. Of those 4,800, 2,600 are in Texas and 1,100 each are in Arizona and California.
The company announced its actions earlier in its investigation than typical "given that we are only one day away from important elections in the USA", he added.
Earlier on Monday, numerous federal agencies, including the FBI, wrote a joint statement alerting Americans to the fact that "foreign actors-and Russian Federation in particular-continue to try to influence public sentiment and voter perceptions through actions meant to sow discord".
The company promised to find out whether these accounts are liked to the Russia-based Internet Research Agency or other foreign entities.
This announcement comes shortly after the authorities and us intelligence agencies announced that they had not spotted any attempts of disruption of the electoral process, but that Americans should be wary of attempts by the russians of spreading false information. The statement detailed government efforts to prevent election interference.
Engaged in its own political campaign of sorts, Facebook has been publicizing its various efforts to curb fake news and political misinformation.
Twitter said on November 3 that it deleted a "series of accounts" that attempted to share disinformation, without providing details.