As Facebook CEO Mark Zuckerberg met Thursday with President Donald Trump and other critics of the tech industry, the Senate's most vocal detractor offered a challenge: Sell your WhatsApp and Instagram properties to prove you're serious about protecting data privacy.

It may have been more than Zuckerberg expected from his private meeting with Sen. Josh Hawley, a conservative Republican from Missouri, in his Capitol Hill office. Zuckerberg left the hourlong meeting — one of several with lawmakers on Capitol Hill — without answering questions from a throng of reporters and photographers pursuing him down a hallway.

Hawley, though, had plenty to say. "The company talks a lot. I'd like to see some action," he told reporters. "I will believe Facebook when I see some real action out of Facebook."

Rather than moving users' personal data from properties such as WhatsApp and Instagram to the core Facebook platform, the company should put a wall around the services or, better yet, sell them off, Hawley said he told Zuckerberg.

Zuckerberg, who requested the meeting, "did not think that was a great idea," he said.

Zuckerberg "had a good, constructive meeting with President Trump at the White House today," a Facebook spokesman said. On Facebook and Twitter, Trump posted a photo with the caption, "Nice meeting with Mark Zuckerberg of Facebook in the Oval Office today."

No details were given on the meeting, first reported by the Axios website.

Trump has persistently criticized social media companies like Facebook, Google, Amazon and his platform of choice, Twitter, embracing conservative critics' accusations that they censor religious, anti-abortion and politically conservative views. Trump has claimed, without evidence, that the companies are "against me" and even suggested U.S. regulators should sue them on grounds of anti-conservative bias.

A Facebook spokesman declined to comment on Hawley's remarks concerning his meeting with Zuckerberg.

The popular services WhatsApp and Instagram are among some 70 companies that Facebook has acquired over the past 15 years or so, giving it what critics say is massive market power that has allowed it to snuff out competition.

Zuckerberg's discussion with Hawley touched on industry competition, data privacy legislation, election security and accusations by conservatives that Facebook and other social media giants are biased against right-leaning content.

During his visit, Zuckerberg also met with other senators including Mark Warner, D-Va., vice chairman of the Senate Intelligence Committee, Mike Lee, R-Utah, a senior member of the Judiciary Committee, and John Cornyn, R-Texas, and Tom Cotton, R-Ark. He also declined to answer reporters' questions when he left Lee's office earlier in the afternoon.

Lee's office said the two discussed bias against conservatives on Facebook's platform, regulation of online services, enforcement of antitrust laws in the tech industry and data privacy issues.

Congress has been debating a privacy law that could sharply rein in the ability of companies like Facebook, Google, Amazon and Apple to collect and make money off users' personal data. A national law, which would be the first of its kind in the U.S., could allow people to see or prohibit use of their data.

Acting preemptively, Zuckerberg last spring called for tighter regulations to protect consumers' data, control harmful online content and ensure election integrity and data portability. The internet "needs new rules," he said.

It was Zuckerberg's first public visit to Washington since he testified before Congress last spring about privacy, election interference and other issues.

Facebook, a social media giant based in Menlo Park, California, with nearly 2.5 billion users, is under heavy scrutiny from lawmakers and regulators following a series of privacy scandals and amid accusations of abuse of its market power to squash competition.

The Justice Department, the Federal Trade Commission and the House Judiciary antitrust subcommittee are all conducting antitrust investigations of the big tech companies, and a bipartisan group of state attorneys general has opened a competition probe specifically of Facebook.

At Facebook's request, Warner helped organize a dinner meeting in Washington on Wednesday night for Zuckerberg and a group of senators.

Warner told The Associated Press he wanted Zuckerberg to hear his Senate colleagues' "enormous concerns about privacy and about protecting the integrity of our political system."

Their message for the Facebook chief was "self-regulation is not going to be the answer," Warner said. "I think Zuckerberg understood that."

Warner and Hawley have proposed legislation that would force the tech giants to tell users what data they're collecting and how much it's worth. The proposal goes to the heart of Big Tech's hugely profitable business model of commerce in users' personal data. The companies gather vast data on what users read and like, and leverage it to help advertisers target their messages to individuals they want to reach.

The tech companies view with particular alarm a separate legislative proposal from Hawley that would require them to prove to regulators that they're not using political bias to filter content. Failing to secure a bias-free audit from the government would mean a social media platform loses its long-held immunity from legal action.