Paris, May 23 (Reuter) - Cuban President Fidel Castro has freed six political prisoners whose release has been requested by an international human rights mission on a rare trip to the Communist island, the groupe France-Libertés said on Tuesday.

A seventh detainee will be treated in hospital, the group said in a statement after visiting Cuba earlier this month.

Castro accepted a request for the mission to travel to Cuba when he visited France in March and met former Socialist president François Mitterrand. Mitterrand's wife Danielle heads the human rights group France-Libertés.

"Mr Fidel Castro has just announced to us the release of the following six prisoners: Rolando Indamiro Restano Diaz, Sebastian Arcos Bergnes, Agustin Figueredo Figuaredo, Pedro Antonio Castillo Ferrer, Ismael Salvia Ricardo, Luis Enrique Gonzales Ogre", the statement said.

It said Omar del Pozo Marrero, suffering high blood pressure, would be treated in hospital.

"The mission's first objective has been achieved. A final report will be issued within three weeks", it said.

The mission, which also included representatives of the International Federation of Human Rights, Doctor of the World (Médecin du Monde) and Human Rights Watch/Americas, met Castro as well as his foreign, interior and justice ministers and was allowed to interview several political prisoners.

In an earlier report, the mission had requested the release of five prisoners only. It said Figueredo Figueredo, del Powo Marrero and Castillo Ferrer should be freed for medical reasons, and Arcos Bergnes and Restano Diaz for humanitarian reasons.

A spokeswoman for France Libertés said the mission added Salvia Ricardo and Gonzales Ogra on a later list.

It said in an earlier report that it had been struck by the severity of sentences given to political prisoners who had not been convicted of acts of violence. Castro denied during his visit that Cuba jailed people merely for political beliefs.

France-Libertés said prisoners complained of "cruel and inhuman" conditions during their interrogation and trial and had not been provided with adequate defence. But all said they were spared physical abuse.

They also complained about prison food and most had lost a lot of wheight, but the mission concluded that "the majority did not show any signs of serious, clinically detectable health problems."