An ex-CIA employee who leaked details of the US’s top-secret phone and internet surveillance has disappeared from his hotel in Hong Kong.

Edward Snowden’s whereabouts were not immediately known on Tuesday, although he was believed to be staying somewhere in Hong Kong. Snowden, who worked as a contractor at the NSA and the CIA, allowed The Guardian and The Washington Post to publish a series of top-secret documents outlining the program.

The program, known as Prism, is run by the US National Security Agency. His leaks led to revelations that the US is systematically seizing vast amounts of phone and web data. The US has begun an investigation into the leak.