The younger sister of Fidel and Raul Castro, Juanita Castro, collaborated with the US Central Intelligence Agency in the early 1960s. Speaking on the US Spanish-language TV channel Univision-Noticias 23, Ms Castro spoke about how she initially supported Fidel Castro's 1959 Cuban Revolution that toppled dictator Fulgencio Batista, but that she became disillusioned by the way her elder brother dealt with political opponents.

The 76-year-old Castro sister, who has not spoken to either of her brothers for more than 40 years, made her revelation on the eve of the publication of her memoirs. The book in Spanish entitled Fidel and Raul, My Brothers, the Secret History is being published today. It was co-written with a Mexican journalist.

Ms Castro describes how she worked to shelter and help those who were being persecuted by Fidel Castro's government in Havana. Many opponents of the regime were executed. When approached by a person close to her and Fidel Castro in 1961 to collaborate with the CIA, she decided to say yes and in this way, began a "long relationship with the arch-enemy of Fidel Castro". In 1964, Ms Castro moved to the US when it became clear her own position was in danger.

Former leader, Fidel Castro, who established a one-party communist system in Cuba after the 1959 Revolution, ruled the island for nearly half a century. Last year, he handed over the presidency to his young brother, Raul, because of health issues.