Testifying before the United States Congress on Tuesday, a former Facebook employee accused the giant tech company of pursuing profits over safety. She urged stricter government oversight to alleviate the dangers Facebook poses, from harming children to inciting political violence to fuel misinformation. Frances Haugen told US lawmakers that the company's sites and apps "harm children, stoke division and weaken our democracy". The 37-year-old former product manager turned whistleblower accused the company of failing to make changes to Instagram after internal research showed apparent harm to some teens and being dishonest in its public fight against hate and misinformation. Haugen's accusations were buttressed by tens of thousands of pages of internal research documents she secretly copied before leaving her job in the company's civic integrity unit. Facebook founder Mark Zuckerberg hit back, saying recent coverage painted a "false picture" of the company. In a letter to staff, he said many of the claims "don't make any sense", pointing to their efforts in fighting harmful content, establishing transparency and creating "an industry-leading research program to under these important issues". "We care deeply about issues like safety, well-being and mental health," he said in the letter, made public on his Facebook page. "It's difficult to see coverage that misrepresents our work and our motives." Facebook is the world's most popular social media site. The company says it has 2.7 billion monthly active users. Hundreds of millions of people also use the company's other products, including WhatsApp and Instagram. Haugen told CBS News on Sunday that she had shared a number of internal Facebook documents with the Wall Street Journal in recent weeks. Using the documents, the WSJ reported that research carried out by Instagram showed the app could harm girls' mental health. This was a theme Haugen continued during her testimony on Tuesday. "The company's leadership knows how to make Facebook and Instagram safer, but won't make the necessary changes because they have put their astronomical profits before people," she said. She criticised Zuckerberg for having wide-ranging control, saying that there is "no one currently holding Mark accountable but himself." And she praised the massive outage of Facebook services on Monday, which affected users around the world. "Yesterday we saw Facebook taken off the internet," she said. "I don't know why it went down, but I know that for more than five hours, Facebook wasn't used to deepen divides, destabilize democracies and make young girls and women feel bad about their bodies." Zuckerberg, in his letter, said the research into Instagram had been mischaracterised and that many young people had positive experiences of using the platform. But he said "it's very important to me that everything we build is safe and good for kids". On Monday's outage, he said the deeper concern was not "how many people switch to competitive services or how much money we lose, but what it means for the people who rely on our services to communicate with loved ones, run their businesses, or support their communities". Haugen also offered thoughtful ideas about how Facebook's social media platforms could be made safer. Haugen, a data expert from Iowa with a degree in computer engineering and a master's degree in business from Harvard, worked for 15 years at tech companies including Google, Pinterest and Yelp prior to being recruited by Facebook. "The company's leadership knows how to make Facebook and Instagram safer but won't make the necessary changes because they have put their astronomical profits before people," Haugen said. "Congressional action is needed," she said. "They won't solve this crisis without your help." Zuckerberg appears to agree with Haugen on the need for updated internet regulations, saying that would relieve private companies from having to make decisions on social issues on their own. "We're committed to doing the best work we can, but at some level the right body to assess tradeoffs between social equities is our democratically elected Congress," Zuckerberg wrote. Democrats and Republicans have shown a rare unity around the revelations of Facebook's handling of potential risks to teens from Instagram, and bipartisan bills have proliferated to address social media and data-privacy problems. But getting legislation through Congress is a heavy slog. The Federal Trade Commission has taken a stricter stance toward Facebook and other tech giants in recent years. Haugen suggested, for example, that the minimum age for Facebook's popular Instagram photo-sharing platform could be increased from the current 13 to 16 or 18. She also acknowledged the limitations of possible remedies. Facebook, like other social media companies, uses algorithms to rank and recommend content to users' news feeds. When the ranking is based on engagement — likes, shares and comments — as it is now with Facebook, users can be vulnerable to manipulation and misinformation. Haugen would prefer the ranking to be chronological. But, she testified, "People will choose the more addictive option even if it is leading their daughters to eating disorders." Haugen said a 2018 change to the content flow contributed to more divisiveness and ill will in a network ostensibly created to bring people closer together. Despite the enmity that the new algorithms were feeding, she said Facebook found that they helped keep people coming back — a pattern that helped the social media giant sell more of the digital ads that generate the vast majority of its revenue. Haugen said she believed Facebook didn't set out to build a destructive platform. "I have a huge amount of empathy for Facebook," she said. "These are really hard questions, and I think they feel a little trapped and isolated." But "in the end, the buck stops with Mark," Haugen said, referring to Zuckerberg, who controls more than 50 percent of Facebook's voting shares. "There is no one currently holding Mark accountable but himself." -- Agencies