Facebook has introduced new privacy features like App Lock in Messenger that will help users prevent others from accessing their private messages.

App Lock adds another layer of security to private messages. The optional feature gives users "confidence to know that if a friend or family member needs to borrow your phone, they won't be able to access your chats".

"Privacy is at the heart of Messenger - where you can be yourself with the people who matter most to you, whether that's through a message, video chat, call or a Messenger Room," said Jay Sullivan, Director of Product Management, Messenger Privacy and Safety.

App Lock, present in the new Privacy settings section, will use device's privacy settings like fingerprint or face authentication to unlock the Messenger app.

"Your touch or face ID is not transmitted to or stored by Facebook. The feature is available today on iPhone and iPad and will come to Android in the next few months," Sullivan said in a statement on Wednesday.

Facebook said it is also working on new controls so Messenger users can decide who can message or call them directly, who goes to their requests folder, and who can't message or call them at all.

This will be similar to the message controls on Instagram.

"We're also exploring more ways to protect your privacy and safety when someone you don't know sends you a message," said Facebook.

The social network will test a feature similar to what exists on Instagram and WhatsApp that blurs images in the message requests folder.

This will give Messenger users the choice to view an image from someone they may not know before replying to the message or blocking or reporting the account.

There are over 1.3 billion Messenger users globally and Messenger is expected to grow to 2.4 billion users by 2021.