Former NSA contractor Edward Snowden is being accused of sharing classified documents with people who were not cleared to receive them. Officials did not describe the charges in detail since the papers have been filed under seal, and are not publically available. NBC's Pete Williams reports.

Federal prosecutors filed espionage charges against alleged National Security Agency leaker Edward Snowden, officials familiar with the process said. Authorities have also begun the process of getting Snowden back to the United States to stand trial.

The charges were filed June 14 under seal in federal court in Alexandria, Va. -- and only disclosed Friday.

Snowden has been charged with three violations: theft of government property and two offenses under the espionage statutes, specifically giving national defense information to someone without a security clearance and revealing classified information about "communications intelligence."

Each of the charges carries a maximum of 10 years in prison.

Snowden, who is a former employee of defense contractor Booz Allen Hamilton, leaked details about far-reaching Internet and phone surveillance programs to The Guardian and The Washington Post earlier this month. He revealed his identity while in Hong Kong, where it is believed he is still hiding.

Top intelligence officials told Congress on Tuesday that the programs made public this month have helped foil more than 50 terrorist plots since Sept. 11, including one to blow up the New York Stock Exchange.

President Barack Obama defended the programs in an interview with Charlie Rose of PBS on Monday. He stressed that it was important to him to set up checks on the system.

Officials said charges against Snowden were delayed because the United States and authorities in Hong Kong have been going back and forth to make certain that whatever charges the U.S. filed would conform to the extradition treaty with Hong Kong.

The U.S. has filed a "provisional arrest warrant," formally asking the police in Hong Kong to arrest Snowden. Because the FBI has no jurisdiction outside U.S. borders, U.S. prosecutors must ask local police to make the arrest.

The arrest would start the formal extradition process in court, which will be governed by Chinese law and could take several months to resolve.

Congressman Peter King, chairman of the Homeland Security Subcommittee on Counterintelligence and Terrorism, backed the attempt to prosecute Snowden.

“I fully support the efforts of the United States government to indict and prosecute Edward Snowden to the fullest extent of the law,” he said. “He has betrayed his country and the government must demand his extradition at the earliest date.”

Andy Tsang, Hong Kong’s police commissioner, said that if an extradition request was sent from a country that had a “mutual legal assistance agreement” with Hong Kong, its government would “handle it in accordance with current Hong Kong laws and systems.”

Simon Young, a professor at Hong Kong University’s faculty of law, suggested it was unclear whether Snowden would win or lose any attempt to fight extradition.

He said theft was listed in the U.S.-Hong Kong extradition treaty. “There is an offence listed in the treaty of unlawful handling of property, but this raises the question as to whether information is property and the answer is not clear,” he said in an email.

He said there was a “catch-all” clause covering “any other offence which is punishable” under both countries’ laws.

But he added that “for legal arguments which I will not go into now, I am doubtful that offenses not specifically mentioned in either the treaty or FOO [Hong Kong’s Fugitives Offenders Ordinance] will be the subject of surrender.”

Young said that elements of the three alleged offenses “exist in neutral terms and cannot necessarily be said to be of a political character.”

“But more important for this exception will be all the surrounding circumstances including the motivation for the prosecution, the unfairness of his trial at home and his likely treatment in custody,” he added.

WikiLeaks founder Julian Assange on Wednesday said members of his anti-secrecy website have been in contact with Snowden's lawyers and are helping him seek asylum in Iceland.

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