Facebook has started blocking links to free speech-based competitor Minds, claiming the website is "unsecure" and advising users not to promote it.

Attempting to send a link to the social network to friends on Facebook will return users with a "security check" notice, which claims Minds is an "unsecure" website and recommends not to send the link.

"To protect your account, we recommend not posting the link. If you want to share it anyway, you'll need to complete this security check," the notice declares, making users complete a CAPTCHA before the link will send.