MOSCOW/HONG KONG (Reuters) - Russia defied White House pressure on Monday to expel former US spy agency contractor Edward Snowden to the United States before he flees Moscow on the next stop of his globe-crossing escape from US prosecution.

Mr Snowden, whose exposure of secret US government surveillance raised questions about intrusions into private lives, was allowed to leave Hong Kong on Sunday after Washington asked the Chinese territory to arrest him on espionage charges.

The 30-year-old flew to Moscow as a transit stop before heading elsewhere, several sources said. But reports he would fly to Cuba were put in doubt when witnesses could not see him on the plane, despite heightened security before take-off.

Ecuador, which has sheltered the founder of the WikiLeaks anti-secrecy organisation, Mr Julian Assange, said it was considering Mr Snowden's request for asylum. There is no direct flight to Quito from Moscow.

"He didn't take the flight (to Havana)," a source at Russia's national airline Aeroflot told Reuters.