People cross a street in front of a monitor showing file footage of Edward Snowden, a former contractor for the U.S. National Security Agency (NSA), with a news tag (L) saying he has left Hong Kong, outside a shopping mall in Hong Kong June 23, 2013. Snowden left Hong Kong on a flight for Moscow on Sunday and his final destination may be Ecuador or Iceland, the South China Morning Post said. REUTERS/Bobby Yip Edward Snowden has left Hong Kong and flown to Moscow on a commercial flight. Edward Snowden has left Hong Kong and flown to Moscow on a commercial flight.

Mr Snowden, 30, left a government safe house in Hong Kong on Sunday morning and boarded the 10.55am Aeroflot flight to Moscow's Sheremetyevo airport.

"Mr Snowden has today left Hong Kong to a third country in a legal and normal way," said a statement from the Hong Kong government.

Mr Snowden was free to leave Hong Kong because no arrest warrant has yet been issued for him by a local court.

On Friday, the United States revealed it had filing three criminal charges against him at a court in Virginia and asked the Hong Kong police to detain Mr Snowden under a joint extradition treaty.

However, the legal process of issuing a Hong Kong warrant for Mr Snowden left a window for the former CIA employee and intelligence contractor to leave the territory.

"The United States previously requested Hong Kong to issue a provisional arrest warrant for Mr Snowden. Because the US request failed to fully comply with the requirements under Hong Kong law, the US Department of Justice was asked to provide further information in consideration of the relevant legal conditions," the Hong Kong government statement added.

"The failure to provide sufficient information in this case meant there was no legal basis to restrict Mr Snowden's departure," it said.

Previously, Mr Snowden has said both that he was willing to go through the Hong Kong legal system and that he would consider asylum elsewhere, particularly in Iceland.

There are no direct flights between Moscow and Reykjavik, with changes in St Petersburg or Oslo if Mr Snowden was to continue his journey.

However, Russia said earlier this month that it would consider sheltering the former CIA employee and intelligence contractor.

Speaking to the Russian newspaper Kommersant, Dmitry Peskov, Vladimir Putin's spokesman, said: "If such an appeal is given, it will be considered. We'll act according to facts."

His comments were widely carried by the Russian media and won support from some Russian politicians.

Hong Kong also said that it had sent a letter to the US to "formally" explain allegations by Mr Snowden that the US had hacked into several computer systems in the territory.