Facebook users on the Android mobile platform are being notified that their messages will soon only be visible via the social network's Messenger app.
Those on an Android mobile or tablet and using a web browser who try to read messages held within Facebook's instant messaging service are being greeted with a notice that their conversations "are moving to Messenger".
"Soon you'll only be able to view your Messages from Messenger", it adds.
Accessing messages has already been disabled within the official Facebook app on mobile.
Facebook said the move was a continuation of a policy it introduced in 2014.
"Using the Messenger app is faster and enables richer interactions. We're continuing to bring the best experiences we can to the 900 million people on Messenger," the social network said.
Some users have expressed concerns over using the app, citing battery life worries.
Facebook has been keen to boost the functionality of Messenger, with founder Mark Zuckerberg saying in 2015 he wanted to make the service a "platform" where it could be used to buy products as well as enable users to interact with businesses.
Earlier this year Facebook demonstrated how it was using artificial intelligence to create 'bots' that could fulfil this task - able to understand human conversation and respond accordingly. Facebook demonstrated the new software being used in Messenger to arrange a delivery date for clothing bought from an online store.
Messenger began accepting payment transactions in the US in 2015.
The app is regarded as a key part of Facebook's future growth, as messaging apps remain hugely popular. The social network also owns fellow messaging service WhatsApp and photo-sharing app Instagram.