Image caption Prosecutors said Harold Nicholson had sneaked notes to his son on napkins from federal prison

A former CIA agent currently serving a jail sentence for espionage is likely to spend eight more years behind bars after pleading guilty to collecting money from former Russian contacts.

Harold Nicholson admitted to using his son to collect a "pension" from the ex-contacts while still in prison.

Prosecutors said he had sneaked notes to his son on crumpled prison napkins.

Nicholson is serving a 23-year term in Oregon after pleading guilty in 1997 to selling secrets to Russia.

Prosecutors have recommended an eight-year sentence for the 58-year-old.

"Harold Nicholson has admitted not only betraying his country, again, but also betraying his family by involving his son Nathaniel in his corrupt scheme to get more money for his past espionage activities," US Attorney Dwight Holton said in a statement.

Nicholson's son allegedly collected $47,000 (£29,000) from Russians in Mexico, Peru and Cyprus as compensation for work his father had performed in the past.

Nathaniel Nicholson, then 24, pleaded guilty last year to his role in the plot. The money he collected was passed to his grandparents and siblings, at the direction of his father.

Harold Nicholson pleaded guilty in 1997 after being paid $300,000 to pass information concerning young CIA recruits and the identities of senior CIA officers to Russia.