A new human rights report offers a blistering assessment of the Justice Department’s role in the fight against terrorism, taking aim at tactics used to identify and prosecute suspects.

In a lengthy examination of U.S. terrorism prosecutions, Human Rights Watch, working with Columbia Law School’s Human Rights Institute, said the FBI and the Justice Department have created a climate of fear in some Muslim communities through the use of surveillance and informants.

The group accused the government of using sting operations, which some critics described as entrapment, to target people with mental or intellectual disabilities and said that such tactics have driven people away from mosques.

“The report clearly shows, in many respects, the American public is being sold a false bill of goods,” said Andrea Prasow, deputy Washington director at Human Rights Watch. “To be sure, the threat of terrorism is real,” she said. “But in many of the cases we documented, there was no threat until the FBI showed up and helped turn people into terrorists.”

Marc Raimondi, a Justice Department spokesman, said: “The Department of Justice has been a steadfast ally of our nation’s civil rights groups for decades. The report itself acknowledges that the legal process used in the cases it highlighted is not only lawful but is also specifically approved by federal judges. . . . We do not and cannot target individuals solely for engaging in activities protected by the First Amendment, which includes free speech and religion.”

Human Rights Watch, represented by Yale University’s Media Freedom and Information Access Clinic, sued the Federal Bureau of Prisons last year to gather accurate information on the number and conditions of prisoners being held on terrorism charges or post-conviction.

Prasow, one of the report’s authors, said the group tried to get the information through public-record requests, but the government was reluctant to comply and Human Rights Watch sued for the information.

Since the attacks of Sept. 11, 2001, more than 500 people, or about 40 cases a year, have been prosecuted in federal courts on terrorism charges. As of October, Human Rights Watch said, U.S. prisons held 475 people indicted in connection with or convicted of terrorism or terrorism-related offenses.

Of those serving sentences, the report said, 49 people were held in high-security prisons, 137 in administrative facilities and 237 in medium- or low-security prisons. According to the report, 44 terrorists were serving time at a supermax prison in Florence, Colo.

Human Rights Watch said some prisoners were being held under harsh conditions that included prolonged solitary confinement and severe restrictions on their communication with family members and others.

As an example of what it called abusive detention conditions, the group cited the case of Pakistani national Uzair Paracha. He was held in solitary confinement for nearly two years before he was convicted in New York in 2006 — on charges of providing material support for terrorism — and sentenced to 30 years.

Paracha had been in contact with top al-Qaeda terrorists, including the nephew of the self-proclaimed mastermind of the 9/11 attacks.

“You could spend days to weeks without uttering anything significant beyond ‘please cut my lights,’ ‘can I get a legal call/toilet paper/a razor,’ etc., or just thanking them for shutting our light,” he said in a letter to Human Rights Watch.

Paracha, 34, was later moved to a medium-security federal prison in Terre Haute, Ind. He is scheduled to be released in 2029.

The report examined 27 federal prosecutions with a total of 77 defendants and documented what it described as the “significant human cost of certain counterterrorism practices, such as aggressive sting operations and unnecessarily restrictive conditions of confinement.”

Human Rights Watch said the cases “raise serious human rights concerns.”

Among the recommendations in the report, Human Rights Watch said the FBI should ensure that investigations are not opened on the basis of “religious behavior, political opinion, or other activity protected by the right to freedom of expression under international law.”

The group also asked that the Bureau of Prisons end prolonged solitary confinement.

Michael P. Kortan, assistant director of the FBI’s Office of Public Affairs, defended the bureau’s record.

“The FBI does not target individuals or groups on the basis of race, ethnicity or religion and engages in outreach with diverse communities to combat all criminal activity, including terrorism,” he said.

Kortan said the use of informants and undercover agents is lawful and subject to “rigorous oversight.” He added that they are “invaluable tools in keeping our communities safe.”