Jeremy Hunt has told Facebook to "stay away from my kids" after it launched a new messaging app aimed at children.
The social network announced on Tuesday it was testing Messenger Kids in the US for those under 13 who cannot sign up for its full service.
The health secretary took to Twitter to condemn the new tool, saying the firm had promised to prevent under-age use of its product.
"Instead they are actively targeting younger children," he wrote.
"Stay away from my kids please Facebook and act responsibly!"
Not sure this is the right direction at all. Facebook told me they would come back with ideas to PREVENT underage use of their product, but instead they are actively targeting younger children. Stay away from my kids please Facebook and act responsibly! https://t.co/XrwfSHsUMj— Jeremy Hunt (@Jeremy_Hunt) December 5, 2017
According to the BBC's North America technology reporter, Dave Lee, the prevention methods to stop under-age children using Facebook are "trivial", meaning more than 20 million under-13-year-olds are thought to be using the network.
Messenger Kids is a simplified version of Facebook's existing messaging app which needs parents to approve any contacts added by their children.
Once confirmed to be safe, friends can do live video chats, send pictures and text each other.
The firm said it offered a more appropriate app, which parents could allow their children to use on tablets and smartphones.
It has not responded directly to Mr Hunt's tweet, but in a blog post, Facebook's Loren Cheng said the company had spoken to thousands of parents and dozens of experts in child development and online safety.