By Vivian Sequera, Havana
FREE after nearly five years' imprisonment, Cuba's best known dissident, Vladimiro Roca, said that his time behind bars confirmed his conviction that the island's political system does not work and must be changed. And change, he insisted, is possible through peaceful means and with President Fidel Castro in power.

"I have never been virulent in my opposition," Roca said a day after being released, two months short of a five-year sentence on charges of inciting sedition and endangering the nation's economy. "I have reaffirmed the conviction that the system has to be changed because it does not work," he said, sitting on a bench outside the doorway of his Havana home.

Roca's release came exactly a week before former US President Jimmy Carter arrives in the communist country for a five-day visit.

Some saw the move as a goodwill gesture to Carter, but Roca said he thought his release was unrelated.

The international group, Human Rights Watch on Monday, applauded Roca's release, but called on the Cuban Government to release more prisoners.

Activists say they currently have more than 240 documented cases of political prisoners in Cuba.

Roca is well known here because his late father, Blas Roca, was a founding member of the Communist Party of Cuba and remains a revered figure. Vladimiro Roca also has roots in the communist government: he was a military pilot who broke with the system in the early 1990s.

Expelled from his State job working with foreign investment, Roca hooked up with three other Cuban professionals who favoured change, engineer Felix Bonne Carcasses, attorney Rene Gomez Manzano and economist Marta Beatriz Roque.

They formed the "Group of Four" and in 1997 published the document that landed them in jail, The Homeland is for All . Their statement criticised a draft document issued by the Communist Party before its national congress that year, saying it focused on the glories of the revolution but offered no pragmatic proposals to the nation's economic ills. The four were convicted behind closed doors in 1999.