Mark Zuckerberg says Facebook's proposed digital currency, Libra, won't launch anywhere in the world until it gets approval from the U.S. regulators.

The social media giant's CEO was testifying to lawmakers in the U.S. House of Representatives on Wednesday about Facebook's vision to transform the way money is sent and received. 

It says its digital currency will help people across the world who don't have easy access to digital bank accounts and credit cards.

"The idea behind Libra is that sending money should be as easy and secure as sending a message. Libra will be a global payment system fully backed by a reserve of cash and highly liquid assets. Now, I believe that this is something that needs to get built," Zuckerberg told the U.S. House Financial Services Committee.

However, that vision is now under threat. In recent weeks, big brands like Mastercard and eBay have dropped out of the non-profit group that will govern Libra.

Zuckerberg's pledge about the U.S. regulators also wasn't enough for some lawmakers.

"As I have examined Facebook's various problems, I've come to the conclusion that it would be beneficial for all if Facebook concentrates on addressing its many existing deficiencies and failures before proceeding any further on the Libra project," said Congresswoman Maxine Waters, the committee's chair.

Zuckerberg isn't the first Facebook executive to be dragged over the coals by the U.S. lawmakers this year. In July, David Marcus, the head of the cryptocurrency project, came up to Capitol Hill and told two committees that Libra would create a "more inclusive" financial system.

However, former U.S. regulators say the social media giant failed to anticipate the regulatory firestorm they would ignite when they announced Libra earlier this year.

"I think Facebook badly miscalculated. The original whitepaper read like a cryptocurrency tech paper that would be a fringe instrument. It never considered the regulatory aspects of trying to launch a major replacement for national currency. They totally blew that part of it," said Paul Kupiec from the American Enterprise Institute in Washington, DC.

As payments giants like Mastercard drop out of the project, analysts say they're also taking decades of international regulatory experience with them.