The new policy will include otherwise legitimate content spread by those same actors, Zuckerberg said.

"It is clear from the evidence that we've collected that those organisations are controlled and operated by" the Internet Research Agency, he added.

In February, the agency known as IRA was among three firms and 13 Russians indicted by US Special Counsel Robert Mueller on charges they conspired to tamper in the presidential campaign and support Trump while disparaging Democratic candidate Hillary Clinton.

Russian media organisation RBC last year reported that FAN and IRA once shared the same street address and had other connections. One of the people that it said made decisions at FAN was indicted by Mueller's office, which is investigating US intelligence agency conclusions that Moscow tried to undermine the democratic process. Russia denies interfering in the elections.

Facebook disclosed in September that Russians used Facebook to meddle in US politics, posting on the social network under false names in the months before and after the 2016 elections.

Zuckerberg said on Tuesday that improved machine learning had helped find connections between the latest posts and IRA. He and Facebook security officials said the company would do the same when they find more legitimate content being pushed out by groups exposed as manipulators.

"We’re going to execute and operate under our principles," Zuckerberg said. "We don’t allow people to have fake accounts, and if you repeatedly try to set up fake accounts to manipulate things, then our policy is to ban all of your accounts."

Zuckerberg said that the standard is high for such retribution toward news organisations and that state-owned media by itself was fine.

The company decided to root out as much as it can of IRA, which was involved with posts including sponsoring fake pages that were pro-Trump, pro-border security and protesting police violence against minorities, among other topics.

The expanded response could provoke a backlash from Russian internet regulators.

Last October, Google followed up on reported connections between FAN and IRA by removing FAN stories from its search index. Media regulator Roskomnadzor asked Google for an explanation, saying that it needed to protect free speech. Google then reinstated FAN, according to reports at the time.

Facebook officials said its accounts and pages in question had 1 million unique followers on Facebook and 500,000 on Instagram, mainly in Russia, Ukraine, and nearby countries such as Azerbaijan and Uzbekistan.

Zuckerberg, who founded Facebook in his college dorm room in 2004, personally kept quiet about the Cambridge Analytica data leak for four days before apologising and outlining steps that he said would help protect personal data.

Loading

The 33-year-old billionaire plans to testify before US lawmakers to explain Facebook's privacy policies, a first for him, a source said last week, although he has so far not committed to doing the same for UK lawmakers.

Britain's data protection authority, the US Federal Trade Commission and some 37 US state attorneys general are investigating Facebook's handling of personal data.

Zuckerberg initially downplayed Facebook's ability to sway voters, saying days after the US elections that it was a "pretty crazy idea" that fake news stories had an influence.

Eventually, though, Facebook's security staff came to the conclusion that the social network was being used by spies and other government agents to covertly spread disinformation among rivals and enemies.

Critics including US Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, have complained Facebook moved too slowly to investigate and counter information warfare.

Loading

Facebook stepped up efforts to shutter fake accounts before a national election last year in France, and has said it will work with election authorities around the world to try to prevent meddling in politics.

The company, which is now one of the main ways politicians advertise to voters, plans to start a public archive showing all election-related ads, how much money was spent on each one, the number of impressions each receives and the demographics of the audience reached.

Facebook is on track to bring that data to US voters before congressional elections in November, Zuckerberg said on Tuesday. Facebook plans to send postcards by US mail to verify the identities and location of people who want to purchase US election-related advertising.

Reuters