A naturalized US citizen was jailed Wednesday for five years for attempting to help Venezuela build a nuclear weapon by passing on secret information, the US Justice Department said.

Scientist Pedro Leonardo Mascheroni, 79, and his wife Marjorie Roxby Mascheroni, 71, had pleaded guilty after they were caught trying to pass on classified information to an FBI agent posing as a Venezuelan government official.

The pair were formerly employed at the Los Alamos National Laboratory (LANL) and had access to classified information. Both had pleaded guilty on numerous counts.

"The public trusts that the government will do all it can to safeguard 'Restricted Data' from being unlawfully transmitted to foreign nations not entitled to receive it," said assistant attorney general for national security John Carlin.

"We simply cannot allow people to violate their pledge to protect the classified nuclear weapons data with which they are entrusted.

"Today's sentencing should leave no doubt that counterespionage investigations remain one of our most powerful tools to protect our national security."

Mascheroni, a physicist originally from Argentina, worked at LANL from 1979 to 1988 and had demanded cash for the secret information.

His wife, who worked there 1981-2010, was jailed in August for a year.

The "Restricted Data" the duo had access to included information concerning the design, manufacture or use of atomic weapons and production of special nuclear material, or use of special nuclear material in the production of energy.

"Our laws are designed to prevent 'Restricted Data' from falling into the wrong hands because of the potential harm to our national security," said New Mexico US Attorney Damon Martinez.

"Those who work at our country's national laboratories are charged with safeguarding that sensitive information, and we must and will vigorously prosecute anyone who compromises our nation's nuclear secrets for profit."

The couple were indicted in September 2010.