Thousands of pro-Trump ads linked to Russian accounts: Facebook

Facebook has turned over its data on ads bought by a Russian company during the 2016 election to Justice Department special counsel Robert Mueller, reports on Wednesday said.

The tech giant gave Mueller's team, which is investigating Russian links in Donald Trump's presidential campaign, copies of the ads as well as the identities of the ads' buyers, a source told Reuters.

The handover of information comes after Facebook revealed earlier on Wednesday that thousands of ads posted on the site over the past two years were linked to fake Facebook accounts based out of Russia.

Facebook's chief security officer Alex Stamos said nearly 500 accounts had spent roughly $150,000 on about 3,000 ads, but that the accounts had since been suspended.

Facebook reportedly informed congressional investigators about the ads on Wednesday, according to media, including The Washington Post and the Miami Herald.

Facebook representatives told House and Senate investigators that a Russian company linked to a Kremlin intelligence operation used fake accounts to buy about $150,000 in ad posts targeting voters during the 2016 presidential campaign.

But a Facebook official said its search was intended to serve only as a starting point and was limited to accounts that could easily be traced to Russian actors - for example, if they were written in Russian or had a Russian Internet address.

The discovery, revealed to investigators for the congressional intelligence committees, marked the first confirmation that Facebook was at least an oblique tool of Russia's election meddling campaign aimed at planting Donald Trump in the White House.

Facebook's chief security officer said a few of the roughly 3,000 ads found in its initial review, purchased over a two-year period beginning in June 2015, referred directly to the presidential campaign and only about 25 per cent were geographically targeted. The ads focused ''on amplifying divisive social and political messages across the ideological spectrum'', including gun rights and immigration, Stamos said in a Facebook news post.

The disclosure, first reported by the Washington Post, is sure to fuel calls for a deeper review by Facebook into whether Russia also may have used other front companies or nonprofit groups to conceal the purchase of additional sponsored ads carrying harshly critical or fake news about Hillary Clinton.

''These disclosures may be the first layer in unravelling Russian efforts to utilise Facebook's platform to influence voting behaviour,'' Jonathan Albright, a Columbia University researcher who focuses on the digital spread of misinformation, told the Miami Herald.

A Facebook official who declined to be identified told the paper the ad purchases were traced to a maze of fake accounts emanating from a single company connected to a Russian ''troll farm'' in St Petersburg that US intelligence agencies have accused of circulating false information or propaganda that tended to benefit Trump.

Facebook, the popular social media network used daily by more than 1.3 billion people worldwide, has come under intense public pressure to take steps to ensure that it does not become an easy vehicle for spreading falsehoods about political candidates.

The congressional committees and special counsel Mueller are investigating whether Trump's presidential campaign may have colluded with Russia's massive cyberattack.

While much has been written about Russia's use of automated commands, known as ''bots,'' to spread fake news about Clinton via Twitter, Facebook's algorithms aren't so easily penetrated. To reach most people's Facebook pages, a nonpaying sender must have been accepted as a ''friend'' by the would-be recipient.

But advertisers routinely buy sponsored ads that arrive near the top of people's private news feeds. Presidential campaigns have adopted this route as a way to target key subsets of the electorate.

In his news post, Facebook's Stamos said the social media giant was able to trace the ads to 470 inauthentic Facebook accounts and pages created ''in violation of our policies.''

''Our analysis suggests these accounts and pages were affiliated with one another and likely operated out of Russia,'' he wrote.

Stamos noted that earlier this year, Facebook announced improved technology for detecting fake accounts, as well as other actions to curb the flow of misinformation over its network.