The outgoing head of Facebook's communications team on Wednesday took responsibility for the controversial hiring of a conservative consulting firm accused of using “black ops” style techniques, acknowledging critics including investor George Soros were targeted.

The announcement by Elliot Schrage, who said in June he was stepping down, came after Facebook's chief operating officer Sheryl Sandberg has pledged a “thorough” review of its use of Definers to deflect criticism from the social networking giant.

She and Facebook chief executive Mark Zuckerberg maintain they were surprised by a New York Times story last week that said the social network was using Definers to link social network critics to liberal financier Soros.

The Hungarian-born US financier and philanthropist is a favourite target of nationalists and anti-Semitic conspiracy theorists.

Schrage taking the hit for the controversy was seen by some as convenient, since he has previously said he was leaving the social network after working there for more than a decade to start a new chapter in his life.

Definers was hired in 2017 as part of an effort to diversify its advisers in Washington, in the face of growing pressure by competitors and media companies for Facebook to be regulated by the government, Schrage said in a message to co-workers posted online.

But its role grew to include looking into Facebook competitors and doing research on Soros funded campaigns.

“Responsibility for these decisions rests with leadership of the Communications team,” Schrage said.

“That's me.”

“I want to be clear that I oversee our Comms team and take full responsibility for their work and the PR firms who work with us,” Sandberg said in comment shared along with Schrage's message.

Sandberg, who had previously stated that she had no recollection of working with Definers, also revealed that a check of what had crossed her desk showed that Definers was mentioned in some material and in a “small number” of emails she received.

Soros research

Definers began looking into Soros after the philanthropist labelled Facebook a “menace to society” in a speech at Davos early this year, according to Schrage.

“We had not heard such criticism from him before and wanted to determine if he had any financial motivation,” Schrage said.

“Definers researched this using public information.”

When a “Freedom from Facebook” campaign later began portrayed as a grassroots coalition, Definers determined that Soros was funding some coalition members and shared what they learned with the press, according to Schrage.

He contended that as pressure intensified on Facebook through this year, the communications team increasingly used Definers and the relationship was “less centrally managed.”

But Schrage joined Zuckerberg and Sandberg in stressing that Definers was not hired to create or spread false stories to help Facebook.

Zuckerberg said Facebook stopped using Definers the day The New York Times story was published.

Zuckerberg stands firm

The post came a day after Zuckerberg said he has no plans to resign, sounding defiant after a rough year for the social platform.

“That's not the plan,” Zuckerberg told CNN Business when asked if he would consider stepping down as chairman.

He also defended Sandberg, who has drawn criticism over her handling of the social media giant's recent crises.

“Sheryl is a really important part of this company and is leading a lot of the efforts for a lot of the biggest issues we have,” said Zuckerberg.

Facebook has stumbled from one mess to another this year as it grappled with continuing fallout from Russia's use of the platform to interfere in the 2016 US presidential election, the Cambridge Analytica scandal in which user data was harnessed in a bid to help candidate Donald Trump, and a huge security breach involving millions of accounts.

Most recently, an investigative piece published last week by The New York Times said Facebook misled the public about what it knew about Russia's election meddling and used a PR firm to spread negative stories about other Silicon Valley companies and thus deflect anger away from itself.