The US justice department has filed criminal charges against a fugitive ex-intelligence analyst who leaked details of a secret surveillance operation.
The charges against ex-National Security Agency (NSA) analyst Edward Snowden include espionage and theft of government property.
In May, Mr Snowden fled to Hong Kong after leaking details of a programme to monitor phone and internet data.
The US is also reported to be preparing an extradition request.
His leaks revealed that US agencies had systematically gathered vast amounts of phone and web data.
The criminal complaint was lodged with a federal court in the Eastern District of Virginia and a provisional arrest warrant had been issued, court documents show.
Mr Snowden was charged with "Theft of Government Property", "Unauthorized communication of National Defense Information Information" and "Willful Communication of Classified Communications Intelligence".
Each of the charges carries a maximum 10-year prison sentence. The complaint is dated 14 June although it was made only public on Friday.
Mr Snowden's whereabouts are unknown since he left his hotel on 10 June, after going public about his responsibility for the leaks.
Hong Kong police have declined to comment on a local newspaper report that he is staying in a police safe house.
The BBC's Katy Watson in Washington says the move shows how seriously the US administration is taking the issue.
Democratic Senator Bill Nelson, a member of the Senate Armed Services Committee, welcomed the charges.
"I've always thought this was a treasonous act,'' he said in a statement. "I hope Hong Kong's government will take him into custody and extradite him to the US."
Correspondents say that although the US and Hong Kong co-operate on law enforcement matters, Mr Snowden's appeal rights could drag out any extradition proceedings.
Beijing influence
Hong Kong, a Special Administrative Region of China, has a high degree of autonomy from Beijing and signed an extradition treaty with the US in 1998.
The debate in Hong Kong over whether Mr Snowden should be handed over to the US continues. Legislator Leung Kwok-hung said Beijing should tell the authorities to protect Mr Snowden from extradition and the people of the territory should "take to the streets" to shelter him.
Beijing is allowed to exert its influence in foreign policy matters, says the BBC's Juliana Liu in Hong Kong, but it cannot order officials to deviate from the law.
Beijing is highly unlikely to intercede in what is likely to be the early stages of a long legal battle, our correspondent adds.
The leaks led to revelations that the US is systematically seizing vast amounts of phone and web data under an NSA programme known as Prism.
Mr Snowden also alleged that US intelligence had been hacking into Chinese computer networks.
He said he had decided to speak out after observing "a continuing litany of lies" from senior officials to Congress.
The leaks have been a severe embarrassment for President Barack Obama's administration.
US officials have since launched a robust defence of the practice by US intelligence agencies of gathering telephone and internet data from private users around the world.
They say Prism cannot be used to intentionally target any Americans or anyone in the US, and that it is supervised by judges.
Earlier this week the head of the NSA, Gen Keith Alexander, told Congress that it had helped to thwart terror attacks.
In another development, the Guardian newspaper has reported that the UK is tapping fibre-optic cables and gathering large quantities of data.
The Guardian says its report is based on more documents released by Mr Snowden and leaked from the UK's electronic eavesdropping agency, GCHQ.
Data from global communications, including internet and phone use, was stored for up to 30 days to be analysed the papers says.