A former Facebook employee has told US lawmakers that the company's sites and apps "harm children, stoke division and weaken our democracy".

Frances Haugen, a 37-year-old former product manager turned whistleblower, heavily criticised the company at a hearing on Capitol Hill.

Facebook has faced growing scrutiny and increasing calls for its regulation.

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".