(CNN) The relentlessly brutal legacy of political repression that marked Fidel Castro's rule in Cuba offset and undermined his achievements, two major human rights groups said on Saturday.

"There are few more polarizing political figures than Fidel Castro, a progressive but deeply flawed leader," said Erika Guevara-Rosas, Americas Director at Amnesty International.

Castro's 'darkest legacy'

"Access to public services such as health and education for Cubans were substantially improved by the Cuban revolution and for this, his leadership must be applauded," Guevara-Rosas said.

"However, despite these achievements in areas of social policy, Fidel Castro's 49-year reign was characterized by a ruthless suppression of freedom of expression."

"The state of freedom of expression in Cuba, where activists continue to face arrest and harassment for speaking out against the government, is Fidel Castro's darkest legacy."

Amnesty said it has documented hundreds of stories from "prisoners of conscience" who were "detained by the government solely for peacefully exercising their right to freedom of expression, association and assembly."

Fewer people get long-term prison sentences "for politically motivated reasons." But, "repression takes new forms in today's Cuba," Amnesty said.

The group cited "the wide use of short-term arrests and ongoing harassment of people who dare to publish their opinions, defending human rights, or challenging the arbitrary arrest of a relative." It also said access to the Internet is limited.

'Draconian rule'

Human Rights Watch says Castro's repression had been "codified in law and enforced by security forces" and "groups of civilian sympathizers tied to the state." It says the system of repression that targeted dissenters is a "dark legacy that lives on even after his death."

It says the government still carries out some of the practices that emerged under his rule: Surveillance, beatings, arbitrary detention, and public acts of repudiation. And that generated a "pervasive climate of fear."

José Miguel Vivanco, Americas director at Human Rights Watch cited Castro's "draconian rule and the harsh punishments.""

"As other countries in the region turned away from authoritarian rule, only Fidel Castro's Cuba continued to repress virtually all civil and political rights," Vivanco said.

Embargo a pretext for repression

The economic embargo imposed by the United States against Cuba failed to force Castro from power. Human Rights Watch said it placed hardships on Cubans and failed to ease repression. The unsuccessful Bay of Pigs invasion and the many assassination attempt s exacerbated relations.

"Rather than isolating Cuba, the policy isolated the US. Castro proved especially adept at using the embargo to garner sympathy abroad, while at the same time exploiting it as a pretext to repress legitimate efforts to reform Cuba from within, dismissing them as US-driven and -funded initiatives," the group said..

The two nations reestablished diplomatic relations in July, and President Barack Obama visited the island this year.

After Castro's death, Obama issued a statement of condolences. He extended "a hand of friendship to the Cuban people," said they "must know they have a friend and partner in the United States of America."

Human Rights Watch called President Obama's new stance toward Cuba "long overdue." That policy includes the normalizing of relations, the easing of strictures on travel and commerce, and urging lawmakers to mull the lifting of the embargo.

"For decades, Fidel Castro was the chief beneficiary of a misguided US policy that allowed him to play the victim and discouraged other governments from condemning his repressive policies," Vivanco said. "While the embargo remains in place, the Obama administration's policy of engagement has changed the equation, depriving the Cuban government of its main pretext for repressing dissent on the island."