UK Home Secretary Priti Patel has urged the parent company of Facebook and Instagram to introduce measures to protect children from online abuse before encrypted messaging is extended on the platforms.
Failing to do so would be a “grotesque betrayal” of children, she said.
The platforms' parent company, Meta, plans to include a feature where messages are accessed and read only by the sender and recipient.
End-to-end encryption is already used on WhatsApp, a messaging app that is also owned by Meta.
The tech company has said it will protect personal data and privacy.
But in a letter published in The Telegraph on Sunday, Ms Patel said an inability to monitor and flag harmful content would put vulnerable people, particularly children, at risk.
"A great many child predators use social media platforms such as Facebook to discover, target and sexually abuse children," she said.
"These protections need to be in place before end-to-end encryption is rolled out around the world."
Meta has said it plans to make end-to-end encryption the default system for all personal calls and messages next year, but there are concerns that the move will hinder investigations into child abuse.
Ms Patel said global tech companies reported more than 29 million suspected cases of child sexual abuse on their platforms.
UK law enforcement deals with about 800 suspects every month, she said.
“If I were to describe the content of some of this filth, you would be deeply distressed. Technology companies need to recognise their moral responsibility to keep children safe,” she said.
She said the UK government has taken steps to improve digital security with its Online Safety Bill but that it was “reasonable to expect” tech companies to use their resources and expertise to tackle the problem.
Ms Patel said she wanted to work with Meta to find solutions.
“While some things are more important than profits, it is actually in the financial interests of technology companies that the public should have confidence that their products and services will not be used to hurt children," she said.
Ms Patel said the government’s cyber security experts set out a variety of online protections, such as the scanning of conversations, that could be introduced, but that tech companies said the measures were intrusive.
A Meta spokesman said the company had “no tolerance for child exploitation” and was focused on solutions that did not require users' private conversations to be monitored.
“We want to prevent harm from happening in the first place, not just detect it after the fact," he said.
"We continue to work with outside experts and law enforcement to help keep people safe online."
