A former Facebook employee has told US authorities that the company's efforts to remove child abuse material from the platform were "inadequate" and "under-resourced".
The allegations are contained in documents seen by BBC News and submitted to the US Securities and Exchange Commission (SEC) two weeks ago.
The anonymous whistleblower says moderators are "not sufficiently trained and are ill-prepared".
"We have no tolerance for this abhorrent abuse of children and use sophisticated technologies to combat it," the tech giant said in a statement.
"We've funded and helped build the tools used by industry to investigate this terrible crime, rescue children and bring justice to victims," it added.
It also added that it has shared its anti-abuse technologies with other companies, the BBC report said.
The revelations come after former insider Frances Haugen told the US Congress earlier this month that Facebook's platforms "harm children, stoke division and harm our democracy".
This week she also gave evidence to the UK parliamentary committee examining the proposed Online Safety Bill.
Senior executives from Facebook, Twitter, Google, YouTube and Tiktok are also due to give evidence.
The latest revelations come from an unnamed whistleblower, with inside knowledge of the teams within Facebook set up to intercept harmful material.