Amnesty International has called for the immediate release of 75 dissidents jailed in a recent crackdown by the Cuban authorities.
Hector Palacios (L) and Oscar Elias Biscet - both jailed for 25 years
The activists were imprisoned for up to 28 years in April for opposing the government of President Fidel Castro.
Amnesty has compiled a 91-page report detailing what it says were summary and unfair trials and protesting at the length of the jail terms.
The human rights organisation accuses the government of applying "harsh, previously unused legislation against individuals peacefully exercising their legitimate right to free expression".
Cuba has defended its actions, saying it was protecting its independence from a United States-funded conspiracy.
The crackdown began after journalists attended a workshop at the residence of James Cason, the head of the US Interests Section in Havana.
Amnesty's report - entitled "Essential measures? Human rights crackdown in the name of security" - says some of those jailed had no history of opposition activity.
Amnesty International UK Director Kate Allen said: "We call on the Cuban Government to reverse this alarming crackdown,
release prisoners and suspend repressive legislation that has been used against peaceful Cuban citizens."
The ferry hijacking led to the first Cuban executions for three years
Amnesty says it has reviewed the legal documents of more than two-thirds of the 75 dissidents' cases.
It says it rejects Havana's claims that those arrested were "foreign agents" endangering Cuban independence and security.
The rights organisation also condemned the execution in April of three members of a gang who hijacked a Cuban ferry one week before.
Amnesty said it feared the executions - the first in three years - could spell an end to a moratorium on capital punishment and might lead to the execution of some of the 52 prisoners on death row.
Ms Allen said: "[Cuba should] guarantee not to execute
further prisoners following its sudden - and disturbing - return to the death penalty."
In addition to jailing the dissidents and execution the hijackers, a Cuban court last month jailed for life five men who attempted to hijack a passenger plane in April.
Three other defendants received jail terms of between 20 and 30 years.
The incidents have sent US-Cuba relations plummeting.
Last month, the US ordered 14 Cuban diplomats serving at the United Nations and in Washington to leave the country, implying they had been spying.
The United States also draws criticism in the Amnesty report.
It says Washington should end its trade embargo on Cuba, saying the policy has had a "negative effect... on the full range of human rights in Cuba".