A campaign group advocating the break-up of Facebook has subverted the social network's advertising tools to tempt its employees into leaking information.

Freedom from Facebook says it targeted ads at the technology company's staff, promoting a "safe space" website where they can anonymously submit "whistleblower tips".

Facebook declined to comment.

But the BBC understands it is not blocking the ads nor keeping a special log of who has viewed them.

The stunt comes a week after the New York Times revealed that a public-relations company used by Facebook had circulated claims that the controversial billionaire George Soros was the hidden backer of the Freedom from Facebook campaign.

Mr. Soros's Open Society Foundations subsequently accused Facebook of conducting a "smear campaign".

Facebook's chief executive, Mark Zuckerberg, and chief operating officer, Sheryl Sandberg, have since said they were unaware of the effort and have ended their contract with Definers, the PR company involved.

However, a leaked internal memo from Facebook's departing communications chief, Elliot Schrage, has since acknowledged he was responsible.

"When the 'Freedom from Facebook' campaign emerged as a so-called grassroots coalition, [our communications] team asked Definers to help understand the groups behind them," the memo - made public by the Techcrunch news site - states.

"They learned that George Soros was funding several of the coalition members. They prepared documents and distributed these to the press to show that this was not simply a spontaneous grassroots movement.

"Responsibility for these decisions rests with leadership of the communications team. That's me."

Mr. Schrage's duties are being taken on by the UK's former Deputy Prime Minister Nick Clegg, who has been charged with carrying out a wider review of Facebook's lobbying efforts.

On Tuesday, Mr. Zuckerberg gave an interview to CNN in which he said he did not see the need to step down from being chairman and hoped that he would work together with Ms Sandberg for "decades more to come".

Micro-targeted ads

Facebook used to have a reputation for having few leaks but that has changed over recent months following the Cambridge Analytica affair and other scandals.

One leak - recently reported by the Wall Street Journal - revealed that an internal survey by Facebook's human resources team had flagged a sharp drop in the percentage of workers who said they were optimistic about its future.

Although Freedom from Facebook has not revealed how it has gone about micro-targeting the workers, there is an option in the company's ad tool to direct a campaign at those who list their employer as Facebook HQ.

It says that close to 89,000 people have done so.

Another alternative would be to use a list of known email addresses belonging to Facebook workers.

The move adds to pressure on the company at a time when it is having to deal with a growing number of controversies.

In recent days alone:

• technical problems temporarily blocked some US and European users having access to their accounts and on Tuesday prevented advertisers launching or making changes to campaigns during the busy run-up to Black Friday
• there has been a spike in the number of members requesting a download of all the data Facebook holds on them. The company has blamed this for delays to processing the submissions. News site Recode suggested this might indicate rising numbers of people are planning to quit Facebook's platforms
• campaigners have criticized it for failing to prevent a 16-year-old girl being sold for marriage in South Sudan via its platform. Facebook did not remove the post involved until more than a fortnight after the sale began despite it being reported in the press in the interim
• there has been a growing backlash against a new auto-comment feature that was found to be prompting users to post comments such as "this is so sad" and "heartbreaking" and prayer-hands emojis in response to reports of a mass shooting in the US. A Next Web editorial said: "The idea that we could adequately communicate empathy through canned messages is reprehensible"
• a Russian company - whose Facebook account was deleted in April as part of a purge of those suspected to be meddling in the US elections - is suing the social network, claiming it is a legitimate news outlet