Facebook said it blocked some 30 accounts on its platform and 85 more on Instagram after police warned they may be linked to "foreign entities" trying to interfere in the US midterm election.
The announcement came shortly after US law enforcement and intelligence agencies said that Americans should be wary of Russian attempts to spread fake news.
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 Russia is accused of manipulating through a vast propaganda campaign in favor of Donald Trump, the eventual winner.
"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," Facebook head of cybersecurity policy Nathaniel Gleicher said in a blog post.
"We blocked these accounts and are now investigating them in more detail."
He added that all the Facebook pages associated with the accounts appeared to be in French or Russian.
Twitter said Saturday it deleted a "series of accounts" that attempted to share disinformation. It gave no number.
Facebook last month said it took down accounts linked to an Iranian effort to influence US and British politics with messages about charged topics such as immigration and race relations. The social network identified 82 pages, groups and accounts that originated in Iran and violated policy on coordinated "inauthentic" behavior.