NBC NEWS: 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 officials did not describe the charges in detail because they've been filed under seal in federal court in Alexandria, Va. The documents are not publicly available.

According to officials, charges accuse Snowden of violating federal espionage laws by sharing classified documents with people who were not cleared to receive them. Charges also accuse him of stealing government property.

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 next step will be for police in Hong Kong to arrest Snowden. That will then start the formal extradition process in court, which could take several months to resolve.

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.