Facebook has reeled in more than 500 million users to its messenger app after forcing many to subscribe to the free service or face not accessing their messages.

The group confirmed that the number of people on its messenger app is more than double that in April.

"Messaging is an important part of how people stay connected and since Messenger launched in 2011 we've been passionate about giving people a faster and more expressive way to communicate," said Facebook's director of product management Peter Martinazzi, this month.

"Messenger was the first of our standalone apps, and unlike our core Facebook apps, it focused on one use case - messaging.

"We've also continued to improve speed and reliability. Updates to Messenger ship every two weeks so it continues to evolve and improve," he added, showing that Facebook plans to stick with the app despite the negative feedback."

In April, Facebook had 200 million people using its free messenger app but the group then told users that they would need to download a separate app to allow them to send videos, make free calls and chat with friends.

The move coincides with Facebook snapping up rival messaging service WhatsApp for $22bn in October this year, which has 600 million monthly users.