The US has criticised Russia and China after fugitive Edward Snowden left Hong Kong for Moscow.
President Barack Obama said the US was pursuing "all the appropriate legal channels" in pursuit of him.
The US has revoked Mr Snowden's passport, and he is thought to have spent the night in an airside hotel at Moscow's Sheremetyevo airport.
On Monday, a seat was booked in his name on a flight to Cuba, but he was not seen on board when it took off.
Gordon Corera reports.
