One of Fidel Castro's sisters has claimed in a new memoir that she spent years collaborating with CIA agents against her brother.

Juanita Castro (76) wrote in My Brothers Fidel And Raul: The Secret Story that she initially backed the overthrow of the Batista dictatorship in 1959.

But she quickly became disillusioned with the new regime and was persuaded by the wife of a Brazilian diplomat to meet American agents.

Her first encounter with the CIA occurred during a trip to Mexico in 1961, shortly after the failed Bay of Pigs invasion, the book claims.

During the meeting with an officer who called himself Enrique she agreed to help the US agency gather information on her brother, but refused to accept money and stated that she would have no part in any violence.

“I want to be very clear that agreeing to collaborate with you does not signify that I will participate in any violent activity against my brother, nor any official in the regime,” she told the agent.

Juanita claims she was asked to smuggle messages, documents and money into Cuba hidden in canned goods as part of her duties.

She eventually fled Cuba in 1964, settling in Miami.

But according to her book, she ended her association with the CIA when Nixon-era agents told her they were no longer going to support the underground fight against Castro.