Facebook has identified a new coordinated political influence campaign to mislead users and organise rallies ahead of November's US congressional elections, taking down dozens of fake accounts on its site, the company has said.

A Russian propaganda arm tried to tamper in the 2016 US election by posting and buying ads on Facebook, according to the company and US intelligence agencies.

Moscow has denied involvement.

Facebook said today that it had removed 32 pages and accounts from Facebook and Instagram, part of an effort to combat foreign meddling in US elections, attempts that lawmakers have called dangerous for democracy.

The company said it was still in the early stages of its investigation and did not yet know who may be behind the campaign to influence this year’s elections.

Chief Operating Officer Sheryl Sandberg said the attempts to manipulate public opinion would likely become more sophisticated to evade its scrutiny, calling it an "arms race."

"This kind of behavior is not allowed on Facebook because we don't want people or organisations creating networks of accounts to mislead others about who they are, or what they’re doing," the company said in a blog post.

More than 290,000 accounts followed at least one of the pages and about $11,000 had been spent on about 150 ads, Facebook said.

The pages had created about 30 events since May 2017, it added.

Facebook identified influence activity around at least two issues, including a counter-protest to a "Unite the Right II" rally set to take place in Washington next week.

The other was the #AbolishICE social media campaign aimed at the US Immigration and Customs Enforcement Agency.

In the blog post, Facebook said it was revealing the influence effort now in part because of the rally.

A previous event last year in Charlottesville, South Carolina, led to violence by white supremacists.

Facebook said it would tell users who had expressed interest in the counter-protest what action it had taken and why.

Officials said that one known account from Russia's Internet Research Agency was a co-administrator of one of the fake pages for seven minutes, but the company did not believe that was enough evidence to attribute the campaign to the Russian government.

The company had previously said that 126 million Americans may have seen Russian-backed political content on Facebook over a two-year period, and that 16 million may have been exposed to Russian information on Instagram.