The US government is hacking Chinese mobile-phone companies to gather data from millions of text messages, Edward Snowden has told the South China Morning Post in Hong Kong.

US spies have also hacked China's Tsinghua University in Beijing and Asia Pacific fibre-optic network operator Pacnet, the newspaper reported on Saturday quoting the former US National Security Agency (NSA) contractor charged with espionage for exposing secret US surveillance activities.

"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 protocol (IP) addresses, over a four-year period.

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

The claims followed soon after a report in the UK's Guardian newspaper 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.

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.

'Network backbones'

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 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 46,000km of fibre and operates in 13 countries, according to its website.

US files charges against NSA leaker

The latest disclosures come amid reports that the US was pressuring Hong Kong to act quickly on its request to extradite Snowden.

"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 on Saturday, speaking on condition of anonymity.

Sources say Snowden, who has been hiding in Hong Kong, has sought legal representation from human rights lawyers as he prepares to fight attempts to force him back to the US to face trial.

Tom Donilon, NSA adviser, told CBS News the US had a "good case" against Snowden and expected Hong Kong to comply with its 1998 extradition treaty with the US.

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

Interim arrest warrant

US authorities had earlier issued a provisional arrest warrant and filed espionage and other charges against Snowden.

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

Snowden was charged with theft of government property, unauthorised communication of national defence information and willful communication of classified communications intelligence information to an unauthorised person, the document said.

Troves of documents leaked by Snowden earlier to the Guardian and the Washington Post revealed that US security services had monitored data about phone calls from Verizon and internet data from large companies such as Google and Facebook as part of counterterrorism efforts.

Snowden is reported to be in hiding in Hong Kong, and the US has also asked Hong Kong to detain Snowden on the provisional arrest warrant, the Washington Post newspaper reported, citing unnamed US officials.

The criminal complaint was filed in the Eastern District of Virginia, where Snowden's former employer, Booz Allen Hamilton, is located, the Post reported.

Source: Agencies