NSA 'records all phone conversations' in unnamed target country

The US National Security Agency is recording every single phone call in one particular country, with the agency able to rewind and review conversations up to a month after they take place, according to people with direct knowledge of the effort and documents supplied by former contractor Edward Snowden.

The programme, called Mystic, began in 2009. Its Retro tool, short for "retrospective retrieval", and related projects reached full capacity against the first target nation in 2011. Planning documents two years later anticipated similar operations elsewhere.

At the request of US officials, The Washington Post is withholding details that could be used to identify the country or other countries where the system's use is envisioned.

In the initial deployment, collection systems are recording "every single" conversation nationwide, storing billions of them in a 30-day rolling buffer that clears the oldest calls as new ones arrive, according to a classified summary.

Analysts listen to only a tiny fraction of the calls, but the absolute numbers are high. Each month, they send millions of voice clippings, or "cuts", for processing and long-term storage.

No other NSA programme disclosed to date has swallowed a nation's telephone network whole.

In a statement, Caitlin Hayden, spokeswoman for the NSA, declined to comment on "specific alleged intelligence activities".