Peter Rafael Dzibinski Debbins, 45, is to be sentenced on February 26, 2021 and faces a maximum penalty of life in prison.

"Debbins today acknowledged that he violated this country's highest trust by passing sensitive national security information to the Russians," Assistant Attorney General John Demers said in a statement.

According to prosecutors, the US-born Debbins was recruited by the Russians as early as 1996, before he had joined the army but after several trips to Russia, the native country of his mother.

"In 1997, Debbins was assigned a code name by Russian intelligence agents and signed a statement attesting that he wanted to serve Russia," the Justice Department said.

Debbins served as an officer in US Army chemical units from 1998 to 2005 before joining the Special Forces.

According to the Justice Department, Russian intelligence agents encouraged him to pursue a career in the Special Forces, where he reached the rank of captain.

"Over the course of the conspiracy, Debbins provided the Russian intelligence agents with... information about his chemical and Special Forces units," the department said.

"In 2008, after leaving active duty service, Debbins disclosed to the Russian intelligence agents classified information about his previous activities while deployed with the Special Forces," it said.

"Debbins also provided the Russian intelligence agents with the names of, and information about, a number of his former Special Forces team members so that the agents could evaluate whether to approach the team members to see if they would cooperate with the Russian intelligence service."

According to the indictment, Debbins was based in Germany and later Azerbaijan with a high-level security clearance.

The last contact with his Russian handlers mentioned in the indictment was in 2011.

That year, according to his LinkedIn profile, Debbins began working for a series of Washington-area defense and intelligence contractors, and studying at a graduate school, the Institute of World Politics, which focuses on national security and intelligence.

The Institute's website described him as a cyber intelligence instructor and a hybrid warfare instructor for the US European Command and NATO.