Facebook has boosting its standalone Messenger app for Apple's iOS and Android with free video calling.

The launch, which Facebook announced on 27 April, follows similar fee video calling over its WhatsApp service.

"Video calling in Messenger is launching today for people on iOS and Android in Belgium, Canada, Croatia, Denmark, France, Greece, Ireland, Laos, Lithuania, Mexico, Nigeria, Norway, Oman, Poland, Portugal, the UK, the US, and Uruguay," Facebook Messenger product head Stan Chudnovsky and engineering manager Param Reddy wrote in the statement. "We'll be rolling out to other regions and locales over the coming months."

The Android and iOS app stores have not yet been updated with the new feature.

"You can quickly start a video call from any conversation with just one tap," Facebook said in a statement.

"If you're messaging with someone and realise that words just aren't enough, you can simply choose the video icon in the top right corner of the screen and start a video call right from within an existing Messenger conversation."

Similar services are offered by Microsoft's Skype, Google Hangouts and Apple's FaceTime.

Facebook last year broke off Messenger from the main Facebook application for mobile users, creating a separate platform which now has some 600 million users.

The world's biggest social network also opened up Messenger to outside developers as part of its strategy to create a "family" of apps that also includes Instagram and WhatsApp.

"Video calling will expand Messenger's real-time communication features, enabling the more than 600 million people who use Messenger every month to reach others wherever they are, from anywhere," the statement said. "It's fast, reliable and high quality."