Facebook has blocked more than 100 accounts it believes may be engaging in “co-ordinated inauthentic behaviour” hours before the midterm elections, launching an investigation into whether the accounts are linked to any foreign entities attempting to interfere in the election.

In an announcement late Monday, Nathaniel Gleicher, Facebook’s head of cybersecurity policy, said the social media giant has so far identified 115 total accounts on Facebook and Instagram that “may be linked to foreign entities.” They include 30 Facebook accounts, mostly in Russian and French, and 85 Instagram accounts, mostly in English. The accounts focused on everything from political debate to celebrities, though it remains unclear the extent to which the users were attempting to influence voters or distribute propaganda, if at all.

Gleicher said the investigation began Sunday evening with a tip from U.S. law enforcement, which discovered the suspicious online activity.

“Typically, we would be further along with our analysis before announcing anything publicly,” Gleicher said in the statement. “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.”

Gleicher said Facebook is probing the suspected accounts to see whether they are linked to foreign entities including the Russia-based internet Research Agency, the shadowy troll farm whose associates have ties to Russian President Vladimir Putin and that was indicted earlier this year in special counsel Robert Mueller’s probe into Russian interference in the 2016 presidential election.

A spokesperson for Facebook declined to disclose any other details about the extent of the current investigation, including which U.S. law enforcement agency tipped off Facebook.

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“Since we are very early in the process, having only gotten the tip less than 24 hours before our announcement, our investigation is still ongoing so we don’t have any additional detail to share at this point,” spokesperson Tom Reynolds said in an email to The Washington Post. “We tried to share everything we could and will update when we have more info.”

The announcement comes as Facebook remains under pressure to purge bots and other foreign actors intent on undermining the U.S. political system from its platforms. Last month, Facebook removed more than 800 pages and accounts that were spreading misinformation seeking to influence public opinion on both the right and left sides of the aisle.

On Monday, the FBI, in a joint statement with the Department of Homeland Security, Justice Department and Director of National Intelligence, said that the agencies had “no indication of compromise of our nation’s election infrastructure that would prevent voting, change vote counts, or disrupt the ability to tally votes.”

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“But Americans should be aware that foreign actors — and Russia in particular — continue to try to influence public sentiment and over perceptions through actions intended to sow discord,” the agencies said. “They can do this by spreading false information about political processes and candidates, lying about their own interference activities, disseminating propaganda on social media, and through other tactics.”

The agencies concluded: “Our agencies have been making preparations for nearly two years in advance of these elections and are closely engaged with officials on the ground to help them ensure the voting process is secure. Americans can rest assured that we will continue to stay focused on this mission long after polls have closed.”

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