Restrictions on civil liberties in Cuba have continued to be harsh since President Raul Castro assumed power from his brother Fidel three years ago, Human Rights Watch said Wednesday.

Authorities have jailed scores of dissidents, protesters and others, often through the use of a "dangerousness" provision that allows the detention of Cubans on suspicion that they might break the law in the future, the rights group said in a 123-page report.

Human Rights Watch said its report, “New Castro, Same Cuba,” is the first broad look at human rights conditions in Cuba since Fidel Castro handed power to his younger brother on a temporary basis in 2006. The ailing older Castro formally stepped down as head of state in February 2008.

Human Rights Watch said liberties remain severely curtailed, despite hope among activists that new leadership in Cuba would end Cold War-era limits on dissent and the media.

In particular, it said Raul Castro has made heavy use of the "dangerousness" law.

"Cubans who dare to criticize the government live under constant fear since they know they could end up in prison just for expressing their opinion," Jose Miguel Vivanco, the group's Americas director, said in a statement issued with the report in Washington.

Nevertheless, the rights group said the United States should lift its 47-year-old embargo on travel and trade with Cuba, calling it a costly failure. It urged more targeted pressure to improve human rights conditions.

"No longer would Cuba be able to manipulate the embargo as a pretext for repressing its own people," the report said.

President Obama has adopted a more conciliatory posture toward Cuba than his predecessor by easing rules restricting travel and money transfers by Cuban Americans. But Obama renewed the embargo as a way to pressure the Cuban government to enact political reforms.

There was no immediate reaction to the report from Cuba, which has denied holding political prisoners and accused foes abroad of stirring discontent in hope of toppling the socialist regime.

ken.ellingwood@latimes.com