Facebook's Public Policy Director Neil Potts testified during a congressional hearing Tuesday about the rise of white nationalism on social networks.

A congressional hearing about the rise of white nationalism that was live streamed on YouTube Tuesday was filled with hate speech, prompting the tech giant to disable comments on the video.

"Hate speech has no place on YouTube. We've invested heavily in teams and technology dedicated to removing hateful comments/ videos," YouTube said in a tweet. "Due to the presence of hateful comments, we disabled comments on the livestream of today's House Judiciary Committee hearing."

The move underscores the challenges that tech companies such as Google and Facebook face as they try to combat hate speech in real time.

Before the hearing started, which was held by the House Judiciary Committee and lasted nearly 4 hours, anonymous YouTube users started making racist and anti-Semitic comments on the platform.

In the most meta thing today, the House Judiciary Committee has a YouTube livestream of its hearing on hate on social media. The live comments are.... full of hate. https://t.co/2ZODaGTcgr pic.twitter.com/us3kNq6Nar

Facebook and Google have been under mounting pressure to do more to combat hate speech on its platform after a white nationalist rally in Charlottesville Virginia in 2017 and a shooting at a Pittsburgh synagogue last year that left 11 people dead and seven injured.

But the problem reached new heights last month after a terrorist opened fire on two mosques in New Zealand, killing 50 Muslims. The gunman live streamed part of the attack on Facebook, but by the time the social network pulled down the video it already spread to other social media sites including Twitter and Google-owned YouTube. The video's spread raised questions about whether efforts to combat hate speech on these platforms are working.

"White nationalism and it's proliferation online have real consequences," said Rep. Jerry Nadler, chairman of the House Judiciary Committee and a New York Democrat. "Americans have died because of it."

The hearing included a variety of witnesses, including officials from civil rights groups that are urging both tech firms and the government to take action against hate speech.

Eileen Hershenov, senior vice president of policy at the Anti-Defamation League, said that the resurgence of white supremacy has been fueled in part by social media sites.

That includes fringe social media sites, such as Gab and 8Chan, a message board that the New Zealand mosque shooter used to share his Facebook Live video.

"These platforms are like round-the-clock digital white supremacist rallies, creating online communities that amplify their vitriolic fantasies," she said.

Officials from Facebook and YouTube tried to assure lawmakers that they've been stepping up their efforts to combat hate speech on the platform, but also emphasized some of the challenges they face. Both companies said they've invested in people and technology to help flag and remove hate speech before it spreads but are also balancing safety with giving people a voice.

Candace Owens, a conservative activist and commentator who testified during the hearing, accused lawmakers of holding the hearing for political gain.

"It's about fear mongering power and control, she said. "It's a preview of a Democrat 2020 election strategy."

Owens was named in a manifesto written by the man accused of carrying out the shootings at two mosques in New Zealand.

Neil Potts, Facebook's public policy director, said that deciding what to keep up or pull down from the world's largest social network isn't always "simple" given the large amount of posts that flow through the site. Facebook has more than 2 billion users worldwide.

Alexandria Walden, counsel for free expression and human rights at Google, said removal of hate speech can be complex because it relies on "spoken rather than visual cues." It's also contentious because there's disagreements of what's considered political speech.

At one point during the hearing, officials from Google and Facebook were asked if they were a neutral platform or an editorial publication.

Potts said that Facebook was a tech company while Walden said Google's YouTube was a "free and open platform" for users to upload their own content.

Questions from lawmakers, though, also highlighted their limited understanding of how the some of the world's biggest tech platforms work. Some asked Facebook whether you can report a post or if Instagram had the same rules as the social network.

On Wednesday, the day after the House hearing, the Senate will meet to discuss "Stifling Free Speech: Technological Censorship and the Public Discourse." Representatives from Facebook, Google and Twitter are expected to attend.

Update, 1:29 p.m. PT: Adds details about Senate hearing next day; Update, April 9 at 6 a.m.: Adds more information about Christchurch attack; Update, April 9 at 11:01 a.m.: Adds background from hearing.

Everything Apple announced: What we know about Apple's TV content and service, credit card, game subscription service and more.

Apple TV Channel's streaming service is here: Get ready for another way to watch your shows in an already crowded battle for your views.