Facebook CEO Mark Zuckerberg has confirmed that special counsel Robert Mueller’s team interviewed the company’s staff about Russian meddling in the 2016 election as a two-day congressional hearing into the social media giant began Wednesday morning.

Mr Zuckerberg said his employees spoke to the Mueller team, but he was not personally interviewed.

“I want to clarify, I’m not sure we have subpoenas. I know we’re working with them,” he said.

Mr Mueller charged 13 Russians and three Russian companies in February with interfering in the US election by sowing discord on social media.

Wearing a dark suit and tie instead of his typical T-shirt and jeans the 33-year-old Mr Zuckerberg opened his testimony with a public apology for the privacy scandal that could jeopardise the future of the social media giant.

In his opening remarks, Mr Zuckerberg told the Senate Commerce and Judiciary committees he took full responsibility for failing to prevent data-mining firm Cambridge Analytica from gathering personal information from 87 million users to try to influence elections.

About one in 50 Australian Facebook users are among those thought to have had their data leaked.

Mr Zuckerberg is using the Senate hearing to try and restore public trust in his company, as well as prevent the imposition of government regulation over the way his company handles user data.

In his opening statement to the inquiry, he also apologised for fake news, hate speech, a lack of data privacy and Russian social media interference in the 2016 elections.

We didn’t take a broad enough view of our responsibility, and that was a big mistake,” Mr Zuckerberg said.

“It was my mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here,” he said.

Mr Zuckerberg said Facebook was “going through a broad philosophical shift.”

As Mr Zuckerberg gave his testimony, Facebook shares closed by up more than 4.5 per cent to end Wall Street trading on almost a two-year high.

Facebook’s stock had dropped almost 11 per cent since news broke of the Cambridge Analytica data leak.

John Thune, chairman of the Senate committee, struck an adversarial tone in his opening remarks.

“In the past, many of my colleagues on both sides of the aisle have been willing to defer to tech companies’ efforts to regulate themselves. But this may be changing,” he said.

Facebook is facing a user backlash over the data breach. Photo: Getty

Outside the Capitol building, which houses the US Congress, online protest group Avaaz set up 100 life-sized cutouts of Zuckerberg wearing T-shirts with the words “Fix Fakebook”.

Facebook faces a growing crisis of confidence among users, advertisers, employees and investors after acknowledging that up to 87 million people, mostly in the US, had personal information harvested from the site by Cambridge Analytica, a political consultancy that has counted US President Donald Trump’s election campaign among its clients. 

It is also struggling to deal with fake news and alleged foreign interference in elections, disclosing in September that Russians under fake names used the social network to try to influence US voters in the months before and after the 2016 election, writing about inflammatory subjects, setting up events and buying ads.

Mr Zuckerberg, who founded Facebook while at Harvard University in 2004, is fighting to prove to critics that he is the right person to go on leading what has grown into one of the world’s largest companies.

On Friday, Zuckerberg threw his support behind proposed legislation requiring social media sites to disclose the identities of buyers of online political campaign ads.

-with agencies