Facebook CEO Mark Zuckerberg endured hours of prickly questioning from lawmakers on Wednesday as he defended the company's new globally ambitious project to create a digital currency while also dealing with widening scrutiny from US regulators.

Representatives also grilled Zuckerberg on Facebook's track record on civil rights, hate speech, privacy and misinformation — not surprising given the litany of scandals Facebook has been dealing with over the past two years.

The House Financial Services Committee's immediate focus was Facebook's plans for the currency, to be called Libra. Zuckerberg took pains to reassure lawmakers that his company won't move forward with Libra without explicit approval from all US financial regulators.

Still, many members of the panel appeared unconvinced.

Rep. Maxine Waters, the California Democrat who chairs the panel, said the Libra project and the digital wallet that would be used with it, Calibra, "raise many concerns relating to privacy, trading risks, discrimination ... national security, monetary policy and the stability of the global financial system."

Furthermore, Waters told Zuckerberg, "You have opened up a discussion about whether Facebook should be broken up."

The social media giant has sparked public and official anger at every turn, from its alleged anticompetitive behaviour to its shift into messaging services that allow encrypted conversations, to its refusal to take down phony political ads or doctored videos.

The breakup spectre — the worst-case scenario for Facebook and other tech behemoths — has been raised by prominent politicians, notably Sen. Elizabeth Warren, a leading Democratic presidential candidate.

The Justice Department, the Federal Trade Commission, the House Judiciary antitrust subcommittee and attorneys general in several states are all conducting investigations of Facebook and other tech giants amid accusations that they abuse their market power to crush competition.

Zuckerberg was on the defensive at the hearing, his first testimony to Congress since April 2018 , parrying criticism but also acknowledging lapses. He conceded at one point that the Libra project is "risky," acknowledging several high-profile companies such as Visa, MasterCard and PayPal had signed on as partners in the currency's governing association but have recently bailed.

Under continued criticism of Facebook's handling of hate speech and potential incitements to violence on its site, he said, "We're not perfect. We make a lot of mistakes."

Trust was a central theme of the hearing. Given Facebook's history "why should congress regulators and the public trust you to create what amounts to the world's largest bank, what really amounts to shadow sovereign government?" asked Rep. Madeleine Dean, a Democrat from Pennsylvania.

Responded Zuckerberg: "Well congresswoman, we are not creating a bank. We are helping an organisation create a payment system."

Zuckerberg held up China as a strong reason for encouraging innovation as embodied in the Libra project.

"While we debate these issues, the rest of the world isn't waiting," he said. "China is moving quickly to launch similar ideas in the coming months."