The United States government is hacking Chinese mobile phone companies to gather data from millions of text messages, former intelligence technician Edward Snowden told the Sunday Morning Post in Hong Kong.

US spies have also hacked China's prestigious Tsinghua University in Beijing and Asia Pacific fibre-optic network operator Pacnet, the Post quoted Snowden as saying.

Snowden, who worked as a contractor for the National Security Agency (NSA), has been charged with espionage by the US after revealing a massive spying programme and has gone to ground after fleeing to Hong Kong.

"The NSA does all kinds of things like hack Chinese cell phone companies to steal all of your SMS data," Snowden said in the interview conducted on June 12.

The Post said Snowden had provided documents listing operational details of specific attacks on computers, including internet protocal (IP) addresses, over a four-year period.

Government data shows almost 900 billion text messages were exchanged in China in 2012.

The claims followed soon after a report in the Guardian in which he claimed the British government's electronic eavesdropping agency had gained secret access to fibre-optic cables carrying global Internet traffic and telephone calls.

Britain's Guardian said that Government Communications Headquarters (GCHQ) had started processing vast amounts of personal information -- including Facebook posts, emails, Internet histories and phonecalls -- and is sharing it with the NSA.

The Post has previously quoted Snowden saying there have been more than 61,000 NSA hacking operations globally, targeting powerful "network backbones" that can yield access to hundreds of thousands of individual computers.

He said these included hundreds of targets in mainland China and Hong Kong.

Snowden told the Post in the report published Saturday that Tsinghua University, which counts China's President Xi Jinping and previous President Hu Jintao among its graduates, was the target of extensive hacking by the US.

The university, which is home to one of the mainland's six major backbone networks from where Internet data from millions of Chinese citizens can be gathered, was breached as recently as January, he said.

In 2009, the NSA also attacked Pacnet, the owner of one of the region's biggest fibre-optic networks, the Post reported, citing information provided by Snowden.

Pacnet, which is headquartered in Hong Kong and Singapore, owns 46,000 kilometres of fibre and operates in 13 countries, according to its website.

A US justice department official has confirmed that a sealed criminal complaint has been lodged with a federal court in Virginia and a provisional arrest warrant has been issued for Snowden, who fled to Hong Kong in May.

But Hong Kong government officials Saturday remained tight-lipped as to whether they had received such a request and whether Snowden had been approached.

"If jurisdictions which have signed an agreement with Hong Kong made a request, then the Hong Kong government would process any request in accordance. And we would deal with it according to the law and system of Hong Kong," Police Commissioner Andy Tsang told reporters.

The Post claimed on its website late Saturday that Snowden remained "safe" in Hong Kong and had not been detained by police.

The city of seven million people has maintained a degree of autonomy since its handover of sovereignty from Britain to China in 1997 and operates a separate legal system.

The former British colony has a long-standing extradition treaty with the US, but Beijing, which has control over the city's defence and foreign affairs, has the potential to veto any ruling.

Legal experts have said that any attempt to extradite Snowden could last several years.

US leaker Snowden charged with espionage: official
Washington (AFP) June 22, 2013 - US authorities have filed espionage charges against rogue intelligence technician Edward Snowden and have asked Hong Kong to detain him, a US official told AFP on Friday.

Confirming a report in the Washington Post, the official said a sealed criminal complaint has been lodged with a federal court in the US state of Virginia and a provisional arrest warrant has been issued.

Snowden was charged with espionage, theft and "conversion of government property." A report on NBC News said he was accused of sharing classified documents with individuals who were not cleared to received them.

Snowden's former employer, Booz Allen Hamilton, a private company that seconded him to work as a contractor for the National Security Agency in Hawaii, is based in Virginia, and prosecutors there often handle security cases.

The 30-year-old technician fled Hawaii on May 20 and flew to Hong Kong, a semi-autonomous Chinese territory, from where he proceeded to leak details of secret US intelligence programs to international media outlets.

The leaks have embarrassed US President Barack Obama's administration, which was forced to defend US intelligence agencies' practice of gathering huge amounts of telephone and Internet data from private users around the world.

Following reports of the sealed complaint, all eyes will turn to Hong Kong and Beijing to see whether China will agree to help the United States by complying with the provisional warrant and holding Snowden.

Hong Kong officials remained tight-lipped on Saturday as to whether Snowden had been approached by the law enforcement authorities or was still a free man.

Police commissioner Andy Tsang told reporters it was "inconvenient" to disclose details of the case.

Tsang insisted any extradition request "has to go through... relevant institutions and also the courts for it to be handled" in the former British colony.

Hong Kong is a semi-autonomous territory with its own legal system and a provision for granting political asylum, but it is subordinate to China in foreign policy matters and has an extradition treaty with Washington.

Snowden has told Britain's Guardian newspaper he might seek asylum in Iceland, which has strong Internet freedom laws, but he is thought to still be in Hong Kong and might now find it difficult to travel.

On Thursday, an Icelandic businessman connected to the activist website WikiLeaks said he was ready to fly Snowden out of Hong Kong and to safety in Iceland on a chartered jet.

But Olafur Sigurvinsson, head of WikiLeaks partner firm DataCell, said Snowden would probably not travel unless he received assurances from Reykjavik he would be protected from extradition.

Iceland has said it held informal talks with an intermediary of Snowden over the possibility of seeking political asylum, but that he must present himself on Icelandic soil.

Observers say the tiny mid-Atlantic state's new center-right coalition may be less willing to anger the United States than its leftist predecessor.

Interior Minister Hanna Kristjansdottir said Tuesday the government did not feel bound by a 2010 resolution by parliament seeking to make the country a safe haven for journalists and whistleblowers from around the globe.

"The resolution is not a part of the laws that apply to asylum seekers," she told public broadcaster RUV.

Snowden claims that he made his revelations to expose the huge size and indiscriminate nature of the surveillance programs carried out by the NSA and by its allies in Britain's GCHQ intelligence listening station.

The Guardian has published leaked documents that appear to show huge quantities of private telephone and Internet data -- such as emails and call records -- have been scooped up with little or no judicial oversight.

But Obama's administration insists the hitherto secret surveillance programs were fully authorized by laws passed by the US Congress in the wake of the 9/11 attacks and amended since.

They also say the surveillance helped thwart up to 50 planned extremist attacks, some of them on US soil, by allowing US agents to track calls and messages to enemy operatives.