Elizabeth Warren
Elizabeth Warren Image Credit: AP

Elizabeth Warren is buying ads on Facebook that falsely claim Mark Zuckerberg has endorsed President Donald Trump - a ploy used to showcase that ads posted by politicians need to be fact-checked.

Democratic presidential candidate's campaign sponsored the posts that were blasted into the feeds of U.S. users of the social network, pushing back against Facebook's policy to exempt politicians' ads from its third-party fact-checking program.

The ad begins with a lie: Facebook's chief executive officer "just endorsed" Trump for re-election. It quickly backtracks to the truth.

"You're probably shocked. And you might be thinking, 'how could this possibly be true?" the ad said. "Well, it's not."

Facebook's fact-checking policy allowed Trump's team to share ads on the social network that allege former Vice President Joe Biden promised Ukraine $1 billion for firing a prosecutor. Biden's campaign has dismissed Trump's allegations as a smear.

"What Zuckerberg 'has' done is given Donald Trump free rein to lie on his platform - and then to pay Facebook gobs of money to push out their lies to American voters," Warren said in the ad.

Biden's campaign has written to both Twitter and Facebook asking for the ads to be taken down, but the platforms refused, according to technology site The Verge. It quoted a Twitter spokesman as saying, "The ad you cited is not currently in violation of our policies."

Facebook's decision to allow Trump's ad contrasts with CNN, which rejected a request by the president's campaign to run what the network called two "demonstrably false" claims.

"If Senator Warren wants to say things she knows to be untrue, we believe Facebook should not be in the position of censoring that speech," Andy Stone, a spokesman for Facebook, said in a statement to CNN on the ads.