Mark Zuckerberg has signalled a seismic shift in Facebook's strategy, away from public posting and towards encrypted private messages that even the company itself cannot read.

In a 3,000 word blog post on his personal Facebook page, Mr Zuckerberg said he expected private messaging on apps such as Messenger and Whatsapp to become "the main way people communicate on the Facebook network".

He pledged to unify the private messaging features across all Facebook's app into one service and to encrypt it so that it cannot be spied upon by governments or by Facebook itself. 

He also vowed never to store users' "sensitive data" in countries with "weak records on human rights" – which could rule out a future...