Facebook said it has discovered the first co-ordinated disinformation campaign designed to influence the US midterm elections but stopped short of identifying Russia as being behind the attempts to interfere in US democracy.

The social network has been working with the FBI on the attempted interference in the November vote, which follows its discovery of the Russian Internet Research Agency campaign to sow division in the US during the last presidential election campaign in 2016.

Facebook removed 32 pages and accounts from both Facebook and Instagram because they were involved in “co-ordinated inauthentic behaviour”, the company said. Almost 300,000 people followed at least one of these pages, created from March 2017 to May 2018. The pages ran about 150 ads at the cost of around $11,000.

Although the company did not accuse Russia of being behind the effort, Mark Warner, a senator and the top Democrat on the Senate intelligence committee, said it was “further evidence that the Kremlin” was using social media to “sow division and spread disinformation”.

Donald Trump has come under heavy criticism for his lukewarm backing of US intelligence findings that Russia was behind online campaigns to influence the 2016 presidential election. During their recent summit in Helsinki, President Vladimir Putin of Russia acknowledged he supported Mr Trump, arguing he advocated warner US-Russian ties.

Charges filed by the justice department in February charged the Russian Internet Research Agency with using social media to promote divisive issues such as Black Lives Matter and allegations of voter fraud.

Facebook’s new disclosures included one page that tried to stir up political tensions by organising a Facebook event for a counter-protest to a “Unite the Right” event in Washington this August. Inviting people to “No Unite Right 2 - DC”, they posted information on locations and transport to encourage people to attend.

Facebook will now inform these potential attenders that the page was part of the co-ordinated campaign. In total, the pages created 30 events, which about 4,700 people marked themselves as interested in attending.

The company said the actors had gone to much greater lengths to disguise their true identities, using virtual private networks and internet phone services and recruiting third parties to run ads on their behalf. It warned that it may never be able to identify the source of the disinformation campaigns with the same level of certainty as it did with the Russian Internet Research Agency.

Nathaniel Gleicher, head of cyber security policy at Facebook, said the company had first identified the accounts two weeks ago and removed them all on Tuesday.

“As we’ve told law enforcement and Congress, we still don’t have firm evidence to say with certainty who’s behind this effort,” he said. “Some of the activity is consistent with what we saw from the IRA before and after the 2016 elections. And we’ve found evidence of some connections between these accounts and IRA accounts we disabled last year.”

Mr Gleicher noted there were differences between the two efforts as well. “While IP addresses are easy to spoof, the IRA accounts we disabled last year sometimes used Russian IP addresses,” he said. “We haven’t seen those here.”

Adam Schiff, the top Democrat on the House intelligence committee, said the revelation by Facebook showed that “malicious foreign actors bearing the hallmarks of previously identified Russian influence campaigns continue to abuse and weaponise social media platforms to influence the US electorate”.

Mr Schiff added that Facebook should continue to “proactively identifying these actors, notifying Congress and law enforcement, and taking necessary steps to remove the foreign influence content”.

The Facebook development comes as US lawmakers continue to express concern that the country is not adequately prepared to fend off attacks ahead of the November congressional midterm elections.

Dan Coats, the US director of national intelligence, earlier this month warned that “the warning lights are blinking red again” over the threat of cyber attacks on US infrastructure.

The most followed Facebook pages were “Aztlan Warriors”, “Black Elevation”, “Mindful Being”, and “Resisters”. Facebook uncovered the pages because one of the IRA accounts that it disabled in 2017 shared a Facebook event hosted by the “Resisters” page and one of the admins for the page previously had an IRA account for just seven minutes.

The Resisters page posted anti-Trump content, including a post showing the president tweeting with a caption: “If Trump wants to beat Barack Obama’s Twitter record for the most liked tweet he only needs to tweet 2 words ‘I resign”.

Both the Resisters page and the Black Elevation page, which included imagery of Huey Newton from the Black Panthers, advertised vacancies for part-time event co-ordinators.

Copyright The Financial Times Limited 2018