Mark Zuckerberg appeared to stumble when confronted with tough questioning by congresswoman Alexandria Ocasio-Cortez, who asked the Facebook CEO if a right-wing news outlet known for its ties to white supremacist groups is an appropriate fact-checking group to help oversee the social media giant's content.

Ms Ocasio-Cortez confronted Mr Zuckerberg during congressional testimony on Wednesday, where the CEO was due to discuss a cryptocurrency favoured by his company. But the Democrat instead chose to grill him about Facebook's decision not to fact check political advertisements, even in cases where messages posted by politicians are clearly wrong.

She also asked about Mr Zuckerberg's previous admission that he dines regularly with conservatives and right-wing personalities, which he said is part of his strategy to ensure he hears a diverse set of opinions.

"Can you explain why you have named the Daily Caller, a publication well documented with ties to white supremacists as an official fact checker for Facebook?" Ms Ocasio-Cortez asked.

Mr Zuckerberg replied that Facebook does not itself appoint fact checkers on its platform, and instead relies on the International Fact Checking Network (IFCN), a fact checking organisation established by the journalism integrity group Poynter.

"You would say that white supremacist tied publications meet a rigorous standard for fact checking?" Ms Ocasio-Cortez responded.

Facebook birthday: 15 defining moments for the social network Show all 15 1 /15 Facebook birthday: 15 defining moments for the social network Facebook birthday: 15 defining moments for the social network Facebook is born On 4 Feb, 2004, 19-year-old Harvard student Mark Zuckerberg launched a website called 'TheFacebook' from his dorm. Within 24 hours the college social network had more than 1,000 users Wikimedia Commons Facebook birthday: 15 defining moments for the social network Winklevoss twins sue Zuckerberg Within one week of launching, fellow Harvard students Cameron Winklevoss, Tyler Winklevoss and Divya Narendra accused Zuckerberg of stealing their idea. It would be four years later when the resulting lawsuit was finally settled Facebook birthday: 15 defining moments for the social network Open for business The social network finally opened it platform to everyone on 26 September, 2006. The move proved the catalyst in supercharging the site's already explosive growth PA Facebook birthday: 15 defining moments for the social network Billion-dollar bid Yahoo offered $1 billion to buy Facebook in September 2006 but Zuckerberg turned it down. 'I don’t know what I could do with the money,' Zuckerberg reportedly said. 'I’d just start another social networking site' Reuters Facebook birthday: 15 defining moments for the social network In the money In September 2009, almost five years since the site launched, Facebook turned a profit for the first time Getty Images/iStockphoto Facebook birthday: 15 defining moments for the social network Taking the lead Facebook overtook MySpace in 2010 to become the world’s most popular social network Facebook birthday: 15 defining moments for the social network Taking on the tech giants In 2011, Google launched its own social network that it hoped would knock Facebook from its perch. Despite its initial success, Google+ ultimately failed and will be shut down completely in 2019 Getty Facebook birthday: 15 defining moments for the social network Facebook goes public On 18 May, 2012, Facebook went public. The initial public offering raised $16 billion – the third largest in US history Facebook birthday: 15 defining moments for the social network Gobbling up the competition Facebook acquired Instagram in April 2012 for $1 billion, consolidating its position as the world's leading social network Reuters Facebook birthday: 15 defining moments for the social network One billion users On 4 October, 2012, Zuckerberg announced that Facebook had hit 1 billion users. 'If you’re reading this: thank you for giving me and my little team the honour of serving you,' he wrote in a blog post Getty Images Facebook birthday: 15 defining moments for the social network Expanding its empire In February 2014 Facebook acquired the messaging app WhatsApp for $19.3 billion REUTERS/Dado Ruvic Facebook birthday: 15 defining moments for the social network Two billion users In June 2017, Facebook passed the 2 billion user milestone REUTERS/Dado Ruvic Facebook birthday: 15 defining moments for the social network Privacy scandal On 17 March 2018, news broke that UK firm Cambridge Analytica had harvested data from around 87 million Facebook users for the purpose of political profiling in the build up to the 2016 US presidential elections Shutterstock Facebook birthday: 15 defining moments for the social network Record profits Despite the scandals and subsequent #DeleteFacebook campaign, Facebook posted record profits just before its 15th anniversary, the equivalent of $7.37 from each of its 2.32 billions users iStock/Independent Facebook birthday: 15 defining moments for the social network Unhappy users A study found that people are happier when they don’t use Facebook, adding to mounting evidence surrounding the impact social media has on mental health Rex Features

At this point, Mr Zuckerberg turned his head away and stared ahead for a moment, appearing to look for some form of guidance.

He then responded: "Congresswoman I would say that we're not the ones assessing that standard, the International Fact Checking Network is the one setting that standard.

The Independent has reached out to IFCN for comment and clarification.

During her five minutes, Ms Ocasio-Cortez also grilled the Facebook CEO on his company's recent declaration that politicians who post political ads with lies would not be fact checks. That decision prompted outrage among politicians, including by leading Democratic presidential contender Elizabeth Warren, who responded by having her campaign post an intentionally false advert to prove the point. Ms Warren has notably called for the breakup of big tech companies like Facebook.

"Could I pay to to target predominantly black zip codes and pay to advertise to them the incorrect election date?" Ms Ocasio-Cortez said.

"No, congresswoman, you couldn't," Mr Zuckerberg replied, before beginning an explanation about newsworthiness that Ms Ocasio-Cortez cut short.

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"But you said you're not going to fact check my ads," she replied.

"If anyone, including a politician is saying things that can cause, that is calling for violence or could risk imminent physical hard or voter or census suppression ... we will take that content down," he said.

She responded asking that there are, then, certain circumstances.

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"Could I run ads targeting Republicans in primaries saying that they voted for the Green New Deal?" she then asked.