The feature expands a collaboration that allowed Facebook users to directly access its site via Tor's browser on personal computers. It comes as policymakers and technology companies debate whether digital privacy should be curbed to help regulators more easily thwart hackers.

Kate Krauss, a spokeswoman for the Tor Project, a group of developers that oversees development of the anonymity software, said Android support could help expand Tor due to Facebook's large following. Facebook has more than 1.5 billion monthly active users.

Tor has no plans to support Facebook's mobile app for Apple Inc's iPhone, Krauss said.

Facebook said in a blog post that a 'sizeable community' has grown around its feature launched in 2014, which allowed users to access its site via Tor on PCs. That has prompted calls for additional Tor support, it added.

Tor is used to hide computer IP addresses, typically by concealing the identity of an Internet user. Its popularity has grown following revelations of US spying on the Internet by former National Security Agency contractor Edward Snowden in 2013.

Using Tor on Android requires a download of Orbot, an app that is used to connect to Tor, and updating Facebook's app settings.