United States diplomats are scrambling to stop former intelligence contractor Edward Snowden from reaching Ecuador and claiming political asylum.
Officials in Washington say Mr Snowden is a national security threat and must come home to answer charges of espionage.
The former contractor for America's National Security Agency leaked classified documents revealing widespread internet and phone surveillance by the US.
The 30-year-old quit his job and fled to Hong Kong with a cache of secret documents earlier in June. He left there on Sunday and has flown to Moscow on an Aeroflot flight.
If news agencies are right about his travel plans, he will fly out of Russia on an early afternoon flight to Havana in Cuba. From there he is booked on another plane to Caracas in Venezuela. These are all points of safety as he travels halfway around the world to Ecuador, trying to avoid any country that might arrest him on behalf of the US, the BBC reports.
The US has annulled Mr Snowden's passport. But there seems to have been a concerted effort by China, Russia and Ecuador to help him escape the net that was closing around him in Hong Kong.
The White House said it expects the Russian government to "look at all options available" to expel Mr Snowden to the US on spying charges - but Russia reportedly said it has "no grounds" to do so.
White House National Security Council spokesperson Caitlin Hayden said the US has also registered strong objections to authorities in Hong Kong and China through diplomatic channels at the decision to let Mr Snowden flee, Reuters reports.
But the Hong Kong government said the US request did not fully comply with its legal requirements and there was no legal basis to restrict Mr Snowden from leaving the city state.
In their statement announcing Mr Snowden's departure, the Hong Kong authorities said they were seeking clarification from Washington about reports of US spying on government computers in the territory.
Ecuadorean Foreign Minister Ricardo Patino said the government had received an asylum request, but gave did not give additional details.
Ecuadorean ambassador Patricio Alberto Chavez Zavala told reporters at a Moscow airport hotel that he would hold talks with Mr Snowden and Sarah Harrison, a WikiLeaks representative.
Ecuador has given political asylum to the founder of anti-secrecy group WikiLeaks, Julian Assange, who has spent more than a year holed up at the country's embassy in London.
