A former US Army Green Beret officer has admitted conspiring with Russian intelligence officers to supply them with sensitive national defence information.

Prosecutors say Mr Debbins, of Gainesville, Virginia, worked with Russian operatives for more than a decade as part of an elaborate spying mission.

At the request of the operatives, Mr Debbins joined the US Army's Special Forces where he served as a captain.

Mr Debbins, who prosecutors say considered himself a "loyal son of Russia", signed a document stating he wanted to serve the country, according to court papers obtained by The New York Times.

Mr Debbins provided Russia with sensitive information because he was "angry" and "bitter" about his military service.  

He also believed the US was "too dominant in the world and needed to be cut down to size".

"Debbins violated this country’s highest trust by passing sensitive national security information to the Russians,” said John C Demers, assistant attorney general for National Security.  

“[He] betrayed his oath, his country, and his Special Forces team members with the intent to harm the United States and help Russia."

Mr Debbins is scheduled to be sentenced on 26 February and faces life in prison.

According to the court documents, Mr Debbins first visited Russia in 1994 when he was 19-years-old. His mother was born in the former Soviet Union.

He made eight other trips to Russia between 1995 and 2010, and met his future wife during one of the early visits.

His wife's father was a military officer in Chelyabinsk, where Mr Debbins took part in an independent study programme in 1996. During this visit, it is alleged, he first made contact with intelligence officers.

Shortly after graduating from the University of Minnesota in 1997, Mr Debbins returned to Russia.

During this visit he again met with the Russian operatives and discussed his military service in the US. He was given the codename "Ikar Lesnikov".

Mr Debbins was an active US Army officer from 1998 until 2005. In 2004 he was deployed to Azerbaijan but removed from his command following an unknown security violation.

He was subsequently stripped of his top-level security clearance and was honourably discharged in 2005.  

Mr Debbins then served in the army's inactive reserve until he was discharged in 2010.

He then lived in Minnesota and worked for a Ukranian steel manufacturer and a transportation company, court documents show.

During his military service, Mr Debbins met frequently with his Russian handlers and is alleged to have given them information about chemical Special Forces units and the names of his ex-colleagues in the Special Forces team.

He was arrested in August this year after federal investigators found evidence that he joined the military at the request of his Russian handlers.