Special counsel Robert Mueller’s office indicted 13 Russian nationals and three foreign “entities” with election meddling Friday; saying the international agents interacted with “unwitting individuals” within the Trump campaign and other political organizations.

The indictment claims Russian nationals intentionally defrauded the US election system by buying advertisements on social media as well as attempting to coordinate with American political groups.

“Some defendants, posing as U.S. persons and without revealing their Russian association, communicated with unwitting individuals associated with the Trump Campaign and with other political activists to seek to coordinate political activities,” said the statement from the special counsel’s office.

“Defendants made various expenditures to carry out those activities, including buying political advertisements on social media in the names of U.S. persons and entities,” it adds.

According to court filings, Mueller believes the Russian nationals purchased upwards of $100,000 of advertisements on Facebook, potentially reaching over 120 million Americans in the run-up to the 2016 election.