A hedge-fund billionaire who helped bankroll both Donald Trump and Steve Bannon and who is a major shareholder in the controversial data firm Cambridge Analytica, donated $2m to a secretive group that targeted swing states during the 2016 election with anti-Muslim adverts on Facebook and Google, according to an investigative watchdog.

Robert Mercer, whose family has reportedly donated $36.6m to Republican candidates since 2010, reportedly gave the money to Secure America Now, an organisation that produced several video advertisements apparently designed to promote anti-Muslim sentiment.

One of the advertisements, which was shown to voters in swing states that included Nevada and North Carolina, showed France and Germany as if run under sensationalised version of Sharia law.

The group’s 2016 tax return showed Mr Mercer was the biggest donor (Open Secrets ) (Open Secrets)

It showed French schoolchildren being trained to fight for Isis and the Mona Lisa painting covered in a burka. It also showed an image of the Eiffel Tower with a Muslim star and crescent.

“Under Sharia law, you can enjoy everything the Islamic State of France has to offer, as long as you follow the rules,” said the narrator of one the adverts, that appeared as if it was a travel promotion.

Last October, Bloomberg News reported that staff from Google and Facebook worked closely with Secure America Now, which spent several million dollars on the election adverts.

Now, the watchdog group Open Secrets has alleged that Mr Mercer was the most significant of just three donors to Secure America Now. The group’s tax return from 2016, showed that the reclusive Mr Mercer, 71, provided $2m to the organisation.

“Most Americans have never heard of the far-right neoconservative nonprofit that ran the ads. It has no employees and no volunteers, and it’s run out of the offices of a Washington DC law firm,” Open Secrets wrote of Secure America Now.

“More importantly, most voters never saw the ads. And that was by design. The group….worked hand in hand with Facebook and Google to target their message at voters in swing states who were most likely to be receptive to them.”

Mr Trump attended a fundraising party for him at Mr Mercer’s home ahead of the 2016 election (AP)

Bloomberg reported the adverts commissioned by Secure America Now were produced by Harris Media, an Austin-based digital advertising firm.

It claimed the content of the videos left some of its employees feeling uneasy. “It was designed to strike fear in people’s hearts,” it quoted one former Harris employee as saying.

Mark Zuckerberg admits ‘my mistake’ as 87m Facebook users could have seen data accessed by Cambridge Analytica

Secure America Now was first established in 2011 to oppose the construction of a community centre and mosque in New York, close to the site of the September 11 attacks. The group’s president is Allen Roth, a longtime political adviser to Ronald Lauder, the heir to the Estee Lauder fortune and a supporter of conservative and pro-Israel causes.

The group’s website says: “Born in grassroots and matured on the internet, we are now a nationwide army of Democrats, Republicans, Independents, conservatives and liberals who share a common concern about our security and our liberty. We know the stakes and we won’t back down.”

The news agency said that since 2011, the organisation was very critical of the administration of Barack Obama’s handling of the 2012 attack on a diplomatic compound in Libya and the nuclear deal struck with Iran.

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In addition to producing the anti-Muslim adverts, during the 2016 campaign, the group also produced made a parody site, Hillary’s Inbox, with fake email chains between the candidate, her advisers and public figures.

Neither Mr Mercer, Facebook, Harris Media or Secure America Now immediately responded to enquiries from The Independent. In a statement, a spokesperson for Google, said: “We have strict policies that govern where we allow Google ads to appear and we enforce these policies vigorously. When we find ads that violate these policies, we immediately disapprove and stop showing them.”

In recent weeks, Mr Mercer has been in the headlines because of his part-ownership of Cambridge Analytica, the company which mined Facebook data and targeted potential voters with advertising. The firm appears to have played a major role not only in Mr Trump’s victory but that of the Brexit campaign in the UK.

Mr Mercer and his daughter Rebekah, also have a major stake in the right wing news site, Breitbart News, and were backers and supporters of Mr Bannon until he fell out with Mr Trump.