The end-to-end encryption protects all text, photo, video and voice communications from eavesdropping - shutting out hackers and criminals, but also law enforcement and intelligence agencies and the Facebook-owned WhatsApp itself.
The announcement could increase tensions between Washington and Silicon Valley over how much tech companies help or hinder law enforcement access to data on their devices or networks.
A high-profile showdown between Apple and US government authorities over access to encrypted data on an iPhone ended last month when the FBI enlisted an outside party to hack the device.
- DPA