Facebook CEO Mark Zuckerberg has hit back at claims the social media giant fuels division, harms children and needs to be regulated.

Mr Zuckerberg said the claim the company puts profits over safety was "just not true".

"The argument that we deliberately push content that makes people angry for profit is deeply illogical," Mr Zuckerberg wrote in a note to Facebook employees.

He then posted the statement on his account, hours after a whistleblower testified before US politicians.

Mr Zuckerberg said: "I don't know any tech company that sets out to build products that make people angry or depressed.

"The moral, business and product incentives all point in the opposite direction."

Earlier, former employee Frances Haugen testified on Capitol Hill after she leaked reams of internal research to authorities and The Wall Street Journal.

"I believe that Facebook's products harm children, stoke division and weaken our democracy," Ms Haugen told a Senate panel.

"Congressional action is needed. They won't solve this crisis without your help," she added.

In her testimony, she emphasised the power held by a service that is tightly woven into the daily lives of billions of users.

She also noted the risks that the social media giant's platforms are fueling a contagion of eating disorders, body-shaming and self-dissatisfaction that is particularly dangerous for young people.

"There are going to be women walking around this planet in 60 years with brittle bones because of the choices that Facebook made around emphasising profit today," she said, referring to the impact of eating disorders.

Mr Zuckerberg said that of all the claims, he was "particularly focused" on the ones about Facebook and children, adding that he was "proud" of the work the company has done to help young people in distress.

He reiterated his own calls, which date back years, for the industry regulations to be updated, repeating Facebook's stance Congress was the "right body" to do that.

After Ms Haugen's testimony some members of Congress agreed with some of her comments.

"Here's my message for Mark Zuckerberg. Your time of invading our privacy, promoting toxic content and preying on children and teens is over," said Senator Ed Markey.

"Congress will be taking action ... we will not allow your company to harm our children, our families and our democracy anymore," he added.

Senator Amy Klobuchar said she sees the whistleblower disclosures as the long-needed push to get Congress moving.

"I think the time has come for action, and I think you are the catalyst for that action," she told Ms Haugen.

US politicians for years have threatened to regulate social media platforms to address criticisms that the tech giants trample on privacy, provide a megaphone for dangerous misinformation and damage young people's well-being.

Facebook has pushed back hard against the Journal stories underpinned by the voluminous internal studies that Ms Haugen leaked, and even before Mr Zuckerberg's post the company fiercely objected to her testimony.

A Facebook statement called her "a former product manager who worked at the company for less than two years, had no direct reports, never attended a decision-point meeting with C-level executives".

"We don't agree with her characterisation of the many issues she testified about," said the statement from Lena Pietsch, director of policy communications.

Ms Haugen, a 37-year-old data scientist from Iowa who has worked for companies including Google and Pinterest, delivered hours of testimony that showed a developed understanding of Facebook's mentality.

"A lot of the changes I'm talking about are not going to make Facebook an unprofitable company," she said.

"It just won't be a ludicrously profitable company like it is today."

She returned repeatedly to the idea that Facebook is a platform where human behaviour was being manipulated to keep people on the app and engaged.

Ms Haugen noted that she believed Facebook was not intrinsically bad, but rather needed external intervention to guide it away from a place that breeds toxicity.