WASHINGTON - The United States said on Saturday it wants Hong Kong to extradite Edward Snowden and urged it to act quickly, paving the way for what could be a lengthy legal battle to prosecute the former National Security Agency contractor on espionage charges.

Legal sources say Snowden, who is believed to be hiding in Hong Kong, has sought legal representation from human rights lawyers since leaking details about secret U.S. surveillance activities to news media.

"If Hong Kong doesn't act soon, it will complicate our bilateral relations and raise questions about Hong Kong's commitment to the rule of law," a senior Obama administration official said, speaking on condition of anonymity.

U.S. National Security Adviser Tom Donilon told CBS News the United States had a "good case" to bring Snowden back to America to face trial and expected Hong Kong to comply with its extradition treaty.

"We have gone to the Hong Kong authorities seeking extradition of Snowden back to the United States," Donilon said.

He added that U.S. law enforcement officials were in a "conversation" with Hong Kong authorities about the issue.

A senior U.S. law enforcement source said extradition "can, of course, be a lengthy legal process" but expressed optimism that Snowden would be sent back to the United States.

The South China Morning Post reported that Snowden was not detained or in police protection - as reported elsewhere - and instead he was in a "safe place" somewhere in Hong Kong.

The paper also quoted Snowden offering new details about America's spy activities, including accusations of U.S. hacking of Chinese mobile phone companies and targeting China's top Tsinghua University.

"The NSA does all kinds of things like hack Chinese cellphone companies to steal all of your SMS (texting) data," Snowden was quoted by the newspaper as saying in a June 12 interview.

Documents previously leaked by Snowden revealed that the NSA has access to vast amounts of internet data such as emails, chat rooms and video from large companies, including Facebook and Google, under a government program known as Prism.

They also showed that the government had worked through the secret Foreign Intelligence Surveillance Court to gather so-called metadata - such as the time, duration and telephone numbers called - on all calls carried by service providers such as Verizon.

On Friday, the Guardian newspaper, citing documents shared by Snowden, said Britain's spy agency GCHQ had tapped fiber-optic cables that carry international phone and internet traffic and is sharing vast quantities of personal information with the NSA.