MENLO PARK, CALIFORNIA — Facebook says that is has uncovered a Russian-funded campaign to spread divisive social and political messages over its network.

The company said $100,000 was spent on around 3,000 ads over a two-year period that ended in May 2017, the BBC reported.

The advertisements did not support any particular candidate, but focused on immigration, race and equal rights.

The ads directed people to 470 accounts that were spreading false news or were in breach of company policies, Facebook said in a blog post.

The accounts have all been shut down, according to Alex Stamos, Facebook's chief security officer.

Facebook believes, though it cannot verify, that the accounts in question belonged to the Internet Research Agency, a pro-Russian group based in St. Petersburg.

The campaign was discovered as part of Facebook's internal investigation after it was criticized for allowing the spread of fake news on the site in the lead up to the 2016 U.S. presidential election.

"We looked for ads that might have originated in Russia, even those with very weak signals of a connection and not associated with any known organized effort.

"This was a broad search, including, for instance, ads bought from accounts with U.S. IP addresses but with the language set to Russian — even though they didn't necessarily violate any policy or law.

"In this part of our review, we found approximately $50,000 in potentially related ad spending on roughly 2,200 ads."