By Stephen Gibbs
BBC correspondent in Havana
The Cuban Government has published a book alleging that the leading Cuban dissident, Elizardo Sanchez, is a government spy.
The claims are a "colossal lie", Sanchez says
It claims he was decorated in the 1990s by Cuba's Ministry of the Interior for uncovering CIA agents working against Fidel Castro.
Mr Sanchez has vehemently denied the allegations.
For 35 years, Elizardo Sanchez has been a public critic of Fidel Castro's government.
This book, written by two Cuban Government journalists, alleges he has been leading a double life and that five years ago he was recruited by the Cuban authorities as a spy.
Mr Sanchez, who spent eight and a half years in a Cuban jail in the 1980s, has dismissed the claims as complete lies.
He did have some difficulty explaining photographs in the book.
One shows him apparently being affectionately greeted by a three star Interior Ministry official.
Another shows him in a park, allegedly meeting a state intelligence officer.
Mr Sanchez says he cannot recall the details of the encounters, but that he has always been happy to meet anyone to improve the human rights situation in Cuba.
Whatever the basis of the allegations, they do confirm the Cuban Government's determination to sow suspicion amongst its opponents.
During the trials last April of 75 dissidents, it emerged that Cuban intelligence had successfully infiltrated many opposition groups.
The Cuban authorities will no doubt be hoping that a dissident movement where no one can trust anyone becomes impotent.