Some of those possibly fraudulent accounts may have been the work of the Russia-based Internet Research Agency or other foreign entities, according to a blog post by Nathaniel Gleicher, head of cybersecurity policy at Facebook.
"On Sunday evening, US law enforcement contacted us about online activity that they recently discovered and which they believe may be linked to foreign entities," wrote Gleicher in his election post on Tuesday, Nov. 6.
Some 30 Facebook accounts and 85 Instagram accounts that appeared suspicious were blocked by Facebook and were being investigated.
"Almost all the Facebook Pages associated with these accounts appear to be in the French or Russian languages, while the Instagram accounts seem to have mostly been in English - some were focused on celebrities, others political debate," said Gleicher. "Typically, we would be further along with our analysis before announcing anything publicly. But given that we are only one day away from important elections in the US, we wanted to let people know about the action we've taken and the facts as we know them today."
Just a couple weeks earlier, Facebook had taken down 82 pages, groups and accounts it said appeared to be Iranian efforts at misinformation in which people posing as U.S. or U.K. citizens made "politically charged" postings.
That comes after reports over the summer that hundreds of other accounts linked to Russia were blocked from the social media site.
Last month, Facebook said it had set up a "war room" to help police the spread of false information and phony accounts on its site.