Facebook Inc.’s (FB.O) co-founder and chief executive officer Mark Zuckerberg has been called to appear before a House panel as fallout continues from the exploitation of data from millions of the site’s users by a political consulting firm linked to President Donald Trump.

The House Energy and Commerce Committee said in a statement Thursday that Zuckerberg, who has said he’s willing to testify about the episode, "is the right witness to provide answers to the American people."

Facebook’s representatives left "many questions" unanswered during a staff-level briefing by company officials Wednesday, panel chairman Greg Walden and its top Democrat Frank Pallone said in the statement. Five other committees are receiving such briefings, and a bipartisan group of lawmakers also have called for Zuckerberg’s appearance.

For nearly two hours Wednesday, the Facebook officials met privately with staffers from both sides of the political aisle, according to two people who attended the meeting. One main question was whether there might be others -- including other "bad actors" -- who might have had access to the same data that consulting firm Cambridge Analytica obtained more than 50 million Facebook profiles.

Staffers, speaking on the condition they not be identified, said the Facebook officials acknowledged that the company doesn’t know how widely disseminated that information might be, or how many copies were made.

In interviews Wednesday, Zuckerberg said he was “open” to testifying before Congress, if he’s the right person to provide the information lawmakers need. But he stopped short of committing to appear.

Zuckerberg broke days of silence on Wednesday with a post on his site and the media interviews outlining fixes. The belated moves failed to satisfy critics.

The uproar over Cambridge Analytica, the data firm that consulted on Trump’s campaign, has sparked new questions about how Zuckerberg could allow his social network to be abused again for political ends after revelations that Russians exploited the platform to interfere in the 2016 presidential campaigns.

Cambridge Analytica had siphoned data from some 50 million Facebook users as it built a election-consulting company that boasted it could sway voters in contests all over the world. While 270,000 users had authorized an academic to use their data for research purposes, according to reports, the researcher allegedly violated privacy rules when he handed the data off to Cambridge Analytica.