STOCKHOLM (AP) — A Norwegian law firm says it has filed a lawsuit asking an Oslo court to ensure that Edward Snowden can travel to Norway to receive an award without risk of being extradited to the United States.

Lawyers at the Schjodt law firm in Oslo said Thursday they filed the petition on behalf of Snowden and the Norwegian PEN group, which has invited him to receive its Ossietsky Prize in November.

Attorney Halvard Helle told the AP that the petition seeks a "declaratory judgment" stating that Snowden, currently in Russia, cannot be extradited to the U.S.

The former National Security Agency contractor in 2013 leaked details of a secret government eavesdropping program and left the country. He faces U.S. charges that could land him in prison for up to 30 years.