WATCH LIVE: Facebook's Mark Zuckerberg faces grilling from senators on Tuesday

Facebook chief Mark Zuckerberg was set for a fiery face-off on Capitol Hill Tuesday as he attempts to quell a firestorm over privacy and security lapses at the social network that have angered lawmakers and the site's two billion users.

ZUCKERBERG IS SCHEDULED TO TESTIFY AT 2:15 P.M. (ET). WATCH LIVE VIDEO, COURTESY OF PBS NEWSHOUR, BELOW:

Zuckerberg, making his first formal appearance at a Congressional hearing, will seek to allay widespread fears ignited by the leaking of private data on tens of millions of users to a British firm working on Donald Trump's 2016 campaign.

The scandal has sparked fresh talk about regulation of social media platforms, and Facebook in the past week has sought to stem criticism by endorsing at least one legislative proposal, which would require better labeling and disclosure on political advertising.

Senator Bill Nelson, one of the lawmakers who met privately Monday with Zuckerberg, said he believes the 33-year-old CEO is taking the matter seriously.

"I believe he understands that regulation could be right around the corner," the Florida Democrat said.

Other lawmakers were less clear about the need for new regulations.

Republican Senator John Kennedy of Louisiana said, "I'm not interested in regulating Facebook. I'm interested in Facebook regulating itself and solving the problems. I come in peace."

Zuckerberg was set to appear before a Senate panel from 1815 GMT, with another session in the House of Representatives Wednesday.

The huge social network has begun alerting some users about whether their data was leaked to the British firm Cambridge Analytica.

Notification is among several steps pledged by Facebook to fix pervasive problems on data security and manipulation of the platform used by some two billion people worldwide.

Senate Judiciary Chairman Charles Grassley said Tuesday's hearing is the first step in an "open dialogue about how we address growing consumer privacy concerns."

"The tech industry has a duty to respond to widespread and growing privacy concerns and restore the public trust. The status quo no longer works," Grassley added.

- Suit and tie -

On Monday, Zuckerberg ditched his trademark T-shirt for a somber dark suit and tie as he made the rounds on Capitol Hill and sounded contrite about Facebook's conduct.

"We didn't take a broad enough view of our responsibility, and that was a big mistake. It was my mistake, and I'm sorry," Zuckerberg said in his written testimony released by the House commerce committee.

"I started Facebook, I run it, and I'm responsible for what happens here."

In his written remarks, Zuckerberg called Facebook "an idealistic and optimistic company" and said: "We focused on all the good that connecting people can bring."

But he acknowledged that "it's clear now that we didn't do enough to prevent these tools from being used for harm as well. That goes for fake news, foreign interference in elections, and hate speech, as well as developers and data privacy."

Zuckerberg said he has called for more investments in security that will "significantly impact our profitability going forward," adding: "I want to be clear about what our priority is: protecting our community is more important than maximizing our profit."

- 'Investigating every app' -

Zuckerberg recounted a list of steps announced by Facebook aimed at averting a repeat of the improper use of data by third parties like Cambridge Analytica, and noted that other applications were also being investigated to determine if they did anything wrong.

"We're in the process of investigating every app that had access to a large amount of information before we locked down our platform in 2014," said Zuckerberg.

"If we detect suspicious activity, we'll do a full forensic audit. And if we find that someone is improperly using data, we'll ban them and tell everyone affected."

Zuckerberg met behind closed doors with Senators Bill Nelson of Florida and Dianne Feinstein of California, among others.