(CNN) The United States has submitted its formal request to the United Kingdom to extradite WikiLeaks founder Julian Assange, according to a US official with knowledge of the matter.

Prosecutors initially charged Assange with a single count of computer intrusion, but last month added 17 new counts, including controversial charges under the Espionage Act for encouraging, receiving and publishing national defense information in concert with former Army intelligence analyst Chelsea Manning.

Such a charge under the Espionage Act has never been successfully prosecuted, according to CNN legal analyst Steve Vladeck.

Now that the formal extradition package is in, the Justice Department is unlikely to mount additional charges against Assange. The submission was first reported by The Washington Post on Monday.

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