Russia and Iran were the leading purveyors of disinformation on Facebook over the past four years, and the American public was the top target, according to a new report by Facebook summing up the social media network's efforts to purge itself of propaganda, NBC News reported.

Facebook says it shut down 150 networks of fake accounts between 2017 and the end of 2020—many of them foreign disinformation efforts aimed at influencing Americans, others created in the U.S. by domestic extremists.

"Influence operations are not new, but over the past several years they have burst into global public consciousness," the report says. "These campaigns attempt to undermine trust in civic institutions and corrupt public debate by exploiting the same digital tools that have diversified the online public square and empowered critical discussions from Me Too to the Black Lives Matter movements."

Russia and other foreign actors are getting better at blurring the lines between foreign and domestic activity by co-opting unwitting domestic groups to amplify narratives designed to divide Americans, the report says.