US-born Peter Rafael Dzibinski Debbins, 45, was recruited by the Russians as early as 1996, before he had joined the army but after several trips to Russia, the native home of his mother, the department added.

While he was still at university he met with Russian agents in Chelyabinsk while he was studying there, telling them he was a "son of Russia" and was politically pro-Russian, according to the allegations.

The next year Debbins -- whom his Russian contacts gave the cover name of Ikar Lesnikov -- married his Russian girlfriend, whose father was a military officer, and he joined the US military.

A few years later he told the Russians he wanted to leave the military, but they pressed him instead to remain and encouraged him to join the special forces.

He did so in 2001, and two years later was made a captain based in Germany and later Azerbaijan with a high-level security clearance.

He left the service in 2005 but was in regular contact with the Russians while involved in business in Minnesota.

The last contact with his Russian handlers mentioned in the indictment was in 2011, when he told them he was moving to Washington.

That year, according to his LinkedIn profile, he 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 describes him as a cyber intelligence instructor and a hybrid warfare instructor for the US European Command and NATO.

Since February, his LinkedIn page says, Debbins has been a professor at Wisconsin International University in Ukraine.

He was charged with one count of conspiracy to supply US defense information to a foreign government, which carries a maximum sentence of life in prison.

"The facts alleged in this case are a shocking betrayal by a former Army officer of his fellow soldiers and his country," said FBI senior counterintelligence official Alan Kohler in a statement.