“He knows regulation could be around the corner,” Mr. Nelson said, adding that Mr. Zuckerberg was forthright and answered questions to the best of his ability. Among the topics the two discussed was Russia’s interference in the 2016 election, when Russian agents used Facebook to spread divisive messages to the American electorate, Mr. Nelson said.
But when asked whether the meeting helped assuage his concerns about Facebook’s privacy violations, Mr. Nelson said, “Count me as skeptical.” He also said it was to be determined whether Facebook would be able to stave off more foreign disruption in the American midterm elections this fall.
“I think he’s trying,” Mr. Nelson said of Mr. Zuckerberg, “but I think if we don’t get our arms around this, none of us is going to have any privacy anymore.”
Staff for Senator John Thune, Republican of South Dakota and chairman of the Senate Commerce Committee, said Mr. Zuckerberg and the senator were scheduled to meet on Monday. In addition, Mr. Zuckerberg met with the Judiciary Committee leaders, Charles E. Grassley, Republican of Iowa, and Dianne Feinstein, Democrat of California, according to a person briefed on the visits, who asked not to be named because the information was not public.
Senator Grassley did not respond to a request for comment. Mr. Thune’s and Ms. Feinstein’s offices confirmed the meetings with Mr. Zuckerberg but declined to elaborate.
Facebook described Mr. Zuckerberg’s interactions with lawmakers as “courtesy meetings” and pointed to Mr. Zuckerberg’s prepared testimony that was released on Monday. In those comments, which were posted by the House Committee on Energy and Commerce, Mr. Zuckerberg reiterated how Facebook needed to do better in data privacy and other matters.
“We didn’t take a broad enough view of our responsibility, and that was a big mistake,” Mr. Zuckerberg said in prepared testimony. “It was my mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here.”
Mr. Zuckerberg added that Facebook must do more to protect its users’ personal information and summarized some of the measures the Silicon Valley company is taking to lock down the data privacy of its more than 2.2 billion members. Those include blocking app developers from gaining access to the data of users who have been inactive for three months, restricting the ability of users to inadvertently share information about others in their networks and adopting stricter permissions guidelines and search features.
On Monday, Facebook also began notifying the 87 million people whose data may have been harvested by Cambridge Analytica by posting a notification that they would see when they logged into the social network. In addition, all Facebook users will see a new feature highlighting which apps they use and which information they have shared with those apps.
In recent days, Facebook also suspended two data analytics companies for inappropriately gathering data from their platform. AggregateIQ, a Canadian firm associated with Cambridge Analytica, was suspended on Friday, Facebook said. The company was accused of using data inappropriately harvested from Facebook to support the “Vote Leave” campaign for Britain to exit the European Union.
AggregateIQ did not respond to a request for comment about its suspension, which was earlier reported by The Financial Times. According to a statement on its website, “AggregateIQ has never managed, nor did we ever have access to, any Facebook data or database allegedly obtained improperly by Cambridge Analytica.”
Facebook also said it had suspended CubeYou for inappropriately harvesting data, using tactics similar those of Cambridge Analytica. The company collected information on Facebook users through quizzes. CNBC, which earlier reported the firm’s suspension, said people had been misled into believing the quizzes would be used for nonprofit academic research; instead, the data was sold to marketers.
“Our apps and activity on Facebook have been subject to regular audits and reviews with the company,” a CubeYou spokeswoman said. She added that the company was in compliance with Facebook’s data policy and rules and that CubeYou’s terms informed users that their data would be used for academic and business research purposes.
Yet even as Facebook suspended data firms and took other actions over data privacy, worries about what can be posted on the social network continued. Facebook confirmed on Monday that it had removed a popular Facebook page with nearly 700,000 followers that was associated with the Black Lives Matter movement after it was discovered to be inauthentic.
A Facebook spokesman said the individual who started the page was not who he claimed to be on Facebook. The inauthentic page was earlier reported by CNN.
In a separate post on Facebook on Monday, Mr. Zuckerberg addressed how the social network was misused by Russians in the 2016 presidential election and said that Facebook would create the commission of researchers to study social media’s impact on elections.
The commission’s goal, Mr. Zuckerberg wrote, “is both to get the ideas of leading academics on how to address these issues as well as to hold us accountable for making sure we protect the integrity of these elections on Facebook.”
The researchers chosen to participate will have access to privacy-protected sets of Facebook data, but only after being vetted by a review board, external privacy experts, and Facebook’s privacy and research review teams. The company said it would not review or approve the researchers’ findings before they are published.
Financing for the project is being provided by, among others, the John S. and James L. Knight Foundation, the Charles Koch Foundation and the Omidyar Network.
Elliot Schrage, Facebook’s vice president for communications and public policy, and David Ginsberg, its director of research, said in a blog post on Monday that the company had made “real progress” in dealing with hoax stories and sham accounts since the 2016 election and the campaign, known as Brexit, to withdraw Britain from the European Union.
“But there is much more to do — and we don’t have all the answers,” they said.