A former US ambassador who pleaded guilty to spying for Cuba for over four decades was sentenced in federal court on Friday to 15 years in prison.

Victor Manuel Rocha, 73, was arrested in December for what US officials called "one of the highest-reaching and longest-lasting infiltrations of the United States government by a foreign agent."

Rocha pleaded not guilty in February to charges of conspiring to act as an agent of a foreign government but later accepted a plea deal with federal prosecutors.

Judge Beth Bloom, after a three-and-a-half hour hearing in Miami on Friday, told Rocha she would give him "the maximum penalty permitted by law."

In addition to the 15-year sentence, Rocha was given a $500,000 fine.

Rocha, a naturalized US citizen originally from Colombia, allegedly began aiding Havana as a covert agent of Cuba's General Directorate of Intelligence (DGI) in 1981, and his espionage activities continued until his arrest, according to US authorities.

Attorney General Merrick Garland, announcing Rocha's arrest in December, said he had "repeatedly referred to the United States as 'the enemy'" and "repeatedly bragged about the significance of his efforts."

Rocha joined the State Department in 1981 and rose through the ranks as a career diplomat, serving in posts in Havana, Buenos Aires, Mexico City and Washington.

Rocha served on the National Security Council from 1994 to 1995 in the administration of president Bill Clinton, and was the ambassador to Bolivia from 2000 to 2002 under Clinton and George W. Bush. He also served as an advisor to the US military command responsible for Cuba.

The criminal complaint against Rocha details how, over multiple meetings with an undercover FBI agent beginning in November 2022, he "behaved as a Cuban agent," praising the communist-ruled island's late leader Fidel Castro and "using the term 'we' to describe himself and Cuba."

"Despite swearing an oath to defend the Constitution of the United States, Rocha betrayed the US by secretly working as a Cuban agent for decades," said Larissa Knapp, executive assistant director of the FBI's National Security Branch.

"After years of lying and endangering national security and US citizens, he finally accepted responsibility for his actions and received the maximum prison sentence."

Numerous espionage cases have marred relations between the two countries, which have been enemies since Cuba's Communist revolution in 1959, at the height of the Cold War.

Rocha's arrest and conviction come around 15 years after the indictment of Walter Kendall Myers and Gwendolyn Myers, an American couple who spied for Cuba for nearly 30 years.

Kendall Myers was sentenced to life imprisonment, while his wife was sentenced to over five years.

And in 2001, military intelligence analyst Ana Montes was arrested on espionage charges, later admitting that she had been gathering intelligence for Cuba for almost a decade.

Cuba has been under a US embargo since 1962, and is on a State Department list of state sponsors of terrorism.