The figures emerge as the UK is among seven nations warning of the impact of end-to-end encryption on public safety online.
Facebook was responsible for 94% of the 69 million child sex abuse images reported by US technology companies last year.
The figures emerged as seven countries, including the UK, published a statement on Sunday warning of the impact of end-to-end encryption on public safety online.
Facebook has previously announced plans to fully encrypt communications in its Messenger app, as well as its Instagram Direct service – on top of WhatsApp, which is already encrypted – meaning no one apart from the sender and recipient can read or modify messages.
But law enforcement agencies fear the move will have a devastating impact on their ability to target paedophiles and protect children online.
Some 16.9 million referrals were made by US tech firms to the National Centre for Missing and Exploited Children (NCMEC) last year, including 69 million images of children being abused – up 50% on the previous year.
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