This year's contest has been portrayed as crucial by both Republicans and Democrats because both chambers of Congress, and the accompanying ability to pass or reject President Donald Trump's agenda, are up for grabs.
Nearly all of the Facebook Pages associated with the blocked accounts appeared to be in French or Russian.
Social media companies say they are now more vigilant against foreign and other potential election interference after finding themselves unprepared to tackle such activity in the US presidential election two years ago.
A study published last week found that misinformation on social media was spreading at a greater rate than during the run-up to the 2016 presidential vote, which Russian Federation is accused of manipulating through a vast propaganda campaign in favor of Donald Trump, the eventual victor.
The social media giant said USA law enforcement flagged the accounts on Sunday, citing "online activity that they recently discovered and which they believe may be linked to foreign entities", according to the statement.
Facebook said its decision to release its preliminary findings stemmed from the fact that "we are only one day away from important elections in the USA".
Facebook has disrupted a disinformation campaign targeting the USA midterm elections first detected by American law enforcement.
Facebook late Monday said it had received a tip from federal law enforcement and responded by taking down 85 Instagram accounts and 30 Facebook accounts.
The social network said it needed to do further analysis to decide if the accounts are linked to Russia's Internet Research Agency or another group.
Facebook established a "war room" in its Menlo Park headquarters, staffed with a team focused on identifying misinformation, monitoring false news and deleting fake accounts that might be trying to influence voters.
Facebook didn't always take the risk of election interference seriously, however.