WikiLeaks founder Julian Assange has urged the world to "stand with Snowden" just hours after the former intelligence contractor was charged with espionage by the US government for leaking details of a secret web surveillance programme.

Assange, who has been living in refuge in the Ecuadorian embassy in London for a year, was scheduled to give a speech to journalists from the building's balcony but postponed his appearance "due to a security situation" and instead released the announcement on Twitter.

"I have been able to work in relative safety from a U.S. espionage investigation," said Assange, of his time in the embassy.

"But today, Edward Snowden's ordeal is just beginning.

"A few weeks ago, Edward Snowden blew the whistle on an ongoing programme - involving the Obama administration, the intelligence community and the internet services giants - to spy on everyone in the world," said Assange.

"As if by clockwork, he has been charged with espionage by the Obama administration."

He accused Barack Obama of "betraying" a generation, and said the effort to find asylum for Snowden must be "intensified."

Snowden is charged with theft and espionage after leaking details of the 'Prism' web surveillance programme to the press, and prosecutors have asked authorities in Hong Kong, where he is believed to be hiding, to begin extradition proceedings.

Assange is currently in a stand-off with British authorities, who have pledged to arrest him and send him to Sweden to face questioning over sex offence allegations if he leaves the confines of the embassy. Assange claims the allegations are politically motivated.

In 2010, his WikiLeaks website published thousands of secret US diplomatic cables leaked by defence analyst Bradley Manning.

"Two dangerous runaway processes have taken root in the last decade, with fatal consequences for democracy," said Assange. "Government secrecy has been expanding on a terrific scale. Simultaneously, human privacy has been secretly eradicated."

He listed Snowden as one of a series of whistleblowers to have been charged over leaking secret information by the Obama administration, alongside Manning, Barrett Brown, Jeremy Hammond, Aaron Swartz, Gottfrid Svartholm and Jacob Appelbaum.

"They are young, technically minded people from the generation that Barack Obama betrayed. They are the generation that grew up on the internet, and were shaped by it.

"The US government is always going to need intelligence analysts and systems administrators, and they are going to have to hire them from this generation and the ones that follow it.

"One day, they will run the CIA and the FBI. This isn't a phenomenon that is going away. This is inevitable.

"The US government is spying on each and every one of us, but it is Edward Snowden who is charged with espionage for tipping us off."

He demanded the US alter its policies, and called for a "brave" country to "stand up for him (Snowden)" and offer him asylum.

"The charging of Edward Snowden is intended to intimidate any country that might be considering standing up for his rights," Assange said.