Facebook chief executive Mark Zuckerberg has kept a low profile as controversy over the political uses of the social media platform has intensified. (Stephen Lam/Reuters)

Lawmakers in the United States and Britain are calling on Facebook chief executive Mark Zuckerberg to explain how the names, preferences and other information from tens of millions of users ended up in the hands of a data analysis firm connected with President Trump's 2016 campaign.

The demands came in response to news reports Saturday about how the firm, Cambridge Analytica, used a feature once available to Facebook app developers to collect information on 270,000 people and, in the process, gain access to data on tens of millions of their Facebook “friends” — few, if any, of whom had given explicit permission for this sharing.

Though both companies have been embroiled in investigations in Washington and London for months, this weekend’s demands have taken on a more personal tone, focusing explicitly on Zuckerberg, who has not testified publicly on these matters in either nation.

“They say ‘trust us,’ but Mark Zuckerberg needs to testify before the Senate Judiciary Committee about what Facebook knew about misusing data from 50 million Americans in order to target political advertising and manipulate voters,” Sen. Amy Klobuchar (D-Minn.) said Saturday night.

Rep. Adam B. Schiff (Calif.), the highest-ranking Democrat on the House Intelligence Committee, echoed the call for Zuckerberg to personally appear for questioning on Capitol Hill.

“I think it would be beneficial to have him come testify before the appropriate oversight committees, and not just Mark but the other CEOs of the other major companies that operate in this space. There's still a lot we're learning about foreign issues on these platforms,” Schiff said in a phone interview Sunday.

Also Sunday, British lawmaker Damian Collins, who has been leading an investigation into political influence in which officials from Cambridge Analytica and Facebook have testified, suggested that neither company has been sufficiently forthcoming.

“I will be writing to Mark Zuckerberg asking that either he, or another senior executive from the company, appear to give evidence in front of the Committee as part our inquiry,” Collins said in his statement. “It is not acceptable that they have previously sent witnesses who seek to avoid asking difficult questions by claiming not to know the answers. This also creates a false reassurance that Facebook's stated policies are always robust and effectively policed.”

Věra Jourová, the justice commissioner for the European Union, described the reports as “horrifying, if confirmed,” in a tweet. Ahead of a scheduled visit to the United States this coming week, she added that she would seek “further clarifications from #Facebook to understand this problem better.”

Facebook declined to comment on the calls for Zuckerberg to testify. The company said in a statement Sunday afternoon that it was renewing efforts to investigate what happened with the data that reached Cambridge Analytica.

“We are in the process of conducting a comprehensive internal and external review as we work to determine the accuracy of the claims that the Facebook data in question still exists. That is where our focus lies as we remain committed to vigorously enforcing our policies to protect people’s information,” said Paul Grewal, Facebook's deputy general counsel, in the statement.

Zuckerberg has kept a low profile as controversy over the political uses of the Facebook platform — especially by a Russian disinformation campaign during the 2016 U.S. presidential race — has intensified. He has written blog posts and spoken by video link from Facebook's headquarters in Menlo Park, Calif. But Zuckerberg has not yet been exposed to the rough-and-tumble of legislative questioning, designating that job to senior attorneys such as general counsel Colin Stretch.

And on Sunday, the tech giant faced fresh criticism for its failure to be forthcoming with lawmakers investigating the matter.

“Sometimes, these companies grow so fast, and get so much good press, they get up high on themselves, that they start to think perhaps they’re above the rules that apply to everybody else,” Sen. Marco Rubio (R-Fla.) said on NBC’s “Meet the Press.”

The new controversy stems from the actions in 2014 and 2015 of a Russian American professor, Aleksandr Kogan, working for Cambridge Analytica. His app, called thisisyourdigitallife, offered personality predictions and billed itself on Facebook as “a research app used by psychologists.”

It gave Kogan access to demographic information about Facebook users — including the names of users, their “likes,” friend lists and other data. Once obtained by Cambridge Analytica, political campaigns could use those profiles to target users with highly tailored messages, ads or fundraising requests.

Facebook suspended Kogan, the parent company of Cambridge Analytica and one other former Cambridge Analytica employee from the social media platform on Friday, hours ahead of news reports on the extent of the data grab. Cambridge Analytica has repeatedly denied wrongdoing or improper use of Facebook data.

“We worked with Facebook over this period to ensure that they were satisfied that we had not knowingly breached any of Facebook’s terms of service and also provided a signed statement to confirm that all Facebook data and their derivatives had been deleted,” Cambridge Analytica said in a statement Saturday.

Facebook has acknowledged that its user data was collected on a vast scale, but it has declined to confirm or deny reports in the New York Times and the Observer of London that information from 50 million users was accessed. Facebook has said that changes it implemented in 2014 and 2015 sharply restricted the ability of app developers to collect data in this way.

Facebook executives throughout the weekend resisted allegations that Cambridge Analytica's actions amounted to a “breach” of its systems because Facebook's systems were not compromised and the app developer worked within the company's terms of service, at least initially.

In a tweet that has since been deleted, Facebook Chief Security Officer Alex Stamos argued on Saturday that developers working on the Android and Apple operating systems allowed access to Facebook “friend” data, and that the app developer did not break into any of the company’s systems. Facebook has said Cambridge Analytica later violated terms by improperly sharing and then failing to destroy the data, despite assurances that it would do so.

But the idea of a “breach” seems have taken root in the public debate and in some news reports. Klobuchar's statement refers to a “major breach.”

Among the thorny issues facing Facebook is its 2011 consent decree with the Federal Trade Commission. That agreement specified that Facebook must give consumers clear and prominent notice and obtain their express consent before their information is shared beyond the privacy settings they have established. Two former FTC officials who crafted the decree said Sunday that Facebook may have violated it, and could now be liable for many millions of dollars in civil fines.

In a statement Saturday, Facebook said, “We reject any suggestion of violation of the consent decree. We respected the privacy settings that people had in place. Privacy and data protections are fundamental to every decision we make.”

Lawmakers on Capitol Hill said the news reports about Cambridge Analytica were troubling.

“The recent revelations about Facebook and Cambridge Analytica raise serious questions about the extent to which the social media giant respected user privacy and whether it violated its consent decree with the FTC,” said Sen. Edward J. Markey (D-Mass.) in a statement. “Facebook and Cambridge Analytical should be made to testify before the Senate Commerce Committee so that we can get to the bottom of these disturbing reports that may impact tens of millions of Americans.”

U.S. lawmakers last fall questioned Facebook and fellow tech giants Google and Twitter over the ways in which Russian agents used major social networking platforms to spread disinformation during the 2016 election.

The hearings emboldened many lawmakers, including Klobuchar and Sen. Mark R. Warner (D-Va.), to call for new regulation of political advertisements that appear on those sites. Their bill has not yet advanced amid sharp partisan divisions over Russia’s role in the election.

In February, British legislators visited Washington to question Facebook, Google and Twitter about “fake news” and the extent of Russian disinformation online, particularly in the wake of Britain's vote to exit the European Union. Members of the House of Commons repeatedly criticized Facebook for failing to answer questions, at times threatening regulation.

One member of Parliament, Jo Stevens, said Facebook’s relationship with its users’ personal data “reminds me of an abusive relationship where there is coercive control going on.” At another point in the hearing, fellow lawmaker Rebecca Pow questioned whether Facebook was a “massive surveillance operation.”

In December, the Wall Street Journal reported that special counsel Robert S. Mueller III had requested documents from Cambridge Analytica, including copies of emails of any company employees who worked on the Trump campaign. On Saturday, a day after Facebook banned Cambridge Analytica, Massachusetts Attorney General Maura Healey (D) said she was opening a probe into Facebook in response to news reports about Cambridge Analytica.