Juan Carlos Herrera Acosta, part of a group of political prisoners released in August following negotiations between the Roman Catholic Church and Cuba's government, charged that the island nation's prisons are "apocalyptic."
He also said he was tortured behind bars, though he did not elaborate and his account could not be verified.
It says complaints by the West about its human rights record are hypocritical in light of evidence America tortured inmates held without charge at Guantanamo Bay, and says U.S. allies in Europe and elsewhere were complicit in helping Washington set up secret prisons to illegally hold terror suspects.
Acosta was arrested in Cuba during a 2003 crackdown on dissent and sentenced to 12 years in prison on charges of treason. He accepted repatriation to Spain as an apparent condition of his release.
Acosta was in Warsaw at the invitation of Polish lawmakers. He urged Poland and other EU countries to put pressure on Cuba to improve its human rights record.