Facebook revealed Tuesday that it removed more than half a billion fake accounts and millions of pieces of violent or obscene content during the first three months of 2018, pledging more transparency while shielding its chief executive from new public questioning about the company's business practices.

The findings, its first public look at internal moderation figures, illustrate the gargantuan task Facebook faces in cleaning up the world's largest social network, where artificial-intelligence systems and thousands of human moderators are fighting back a wave of offensive content and abuse.

"My top priorities this year are keeping people safe and developing new ways for our community to participate in governance and holding us accountable," wrote Facebook CEO Mark Zuckerberg in a post, adding: "We have a lot more work to do."

Along with fake accounts, Facebook said in its transparency report that it had removed 21 million pieces of content featuring sex or nudity, 2.5 million pieces of hate speech and almost 2 million items related to terrorism by Al Qaida and ISIS in the first quarter of 2018.

Though Facebook extolled its forcefulness in removing content, the average user may not notice any change. For every 10,000 views of content on Facebook, the company said, roughly 8 of them were removed for featuring sex or nudity in the first quarter, up from 7 views at the end of last year.