Husband and wife used the codenames David and Deborah

Carlos Alvarez, 61, and his 56-year-old wife, Elsa, received a five and three-year term respectively for exchanging coded messages with Cuba.

Both said they took responsibility for their actions but had wanted to establish an open dialogue with Cuba.

But a Miami district judge said that their behaviour had undermined US foreign policy towards the country.

"As we know, a good motive is never an excuse for criminal conduct," Miami Judge Michael Moore said before he sentenced the couple.

The pair were accused of sending coded messages about fellow Cuban-American exiles living in Miami back to Cuba.

Carlos Alvarez was accused of being in contact with Cuban intelligence agencies since 1977.

'Innocuous information'

The psychology professor, based at Florida International University, disguised his identity using the codename David.

His wife also communicated with Cuban agents under the name Deborah but to a lesser extent than her husband.

Before being sentenced, Carlos Alvarez told the court he had once been part of an underground movement that sought to oust Castro's regime but that he later became "an advocate of dialogue."

"I decided to engage in a relation that would require sharing what I consider innocuous information and analysis for access," he said, adding, "The method and channel that I used were unfortunately wrong."

Carlos Alvarez's lawyer claimed that the messages included no secret, classified or defence material and often amounted to no more than "simple gossip".

But US lawyer Matthew Axelord said that the pair had gone to great lengths to conceal their actions.

"This was not idle chit-chat," he said, "Carlos Alvarez was tasked directly by the Cuban intelligence service to provide certain information and he provided that information."