Palestinian journalists have been subjected to detention and abuse at the hands of Palestinian security agencies, a pattern that has led many to self-censor and produced a chilling effect on the free exchange of information and ideas, a human rights group said in a new report.

The group, Human Rights Watch, says in the report, titled “No News Is Good News,” that scores of journalists have been improperly detained and harassed in the West Bank under the Palestinian Authority. It calls on the United States and Europe to condition their support for Palestinian security agencies on the authority’s agreeing to take effective steps to investigate and punish those responsible for torture and other serious abuses.

The report, released on Wednesday, focuses on the West Bank, where the United States has given nearly $400 million to the security forces in the past few years. But it also accuses Hamas, which rules in Gaza, of harassment and disruption of free expression by banning unfriendly media and detaining journalists.

In both places, the study says, the central issue is the battle between Hamas and the Fatah-dominated Palestinian Authority. The Palestinian Authority has banned journals and broadcast outlets associated with Hamas; Hamas has banned from Gaza those associated with Fatah.

In the seven West Bank cases examined in some depth in the report, the organization said the “harassment and abuse of journalists reflected attempts to prevent free speech and inquiry into matters of public importance, and to punish writers solely because of their statements critical of the Palestinian Authority or their perceived support of its political rivals.”

Prime Minister Salam Fayyad of the Palestinian Authority said he had not yet read the report. But, Mr. Fayyad said by telephone: “Protection of freedoms, especially freedom of expression, is definitely something we see as a matter of priority. We have a politically charged situation, and there are security challenges. But if abuses have occurred, we will demand accountability.”

Abdel Nasser al-Najjar, president of the Palestinian Journalists Syndicate, said he believed the violations of journalists’ rights that had occurred “were based on security apparatus decisions at a time when the president and prime minister were giving clear instructions not to violate Palestinian media rights.”

A vast majority of the abuse cases examined by Human Rights Watch involved the intelligence services, but at least one allegedly involved members of the National Security Forces who are trained and equipped by the United States. Training in human rights is an integral part of what is provided.

In one case, Muhanad Salahat, a freelance writer and filmmaker, was detained just over a year ago, but not notified of the reason. He was held for 14 days without charge and interrogated twice daily about his work on documentaries for Al Jazeera, the satellite channel, opinion articles published online and his membership in a Facebook group.

He went on a hunger strike, which led to his release. Friends said they had been told he had been arrested for forging checks.

In Gaza, the report said, security officials harass some reporters whose work they consider critical of Hamas policy, visiting their homes and confiscating or breaking their equipment. Most recently, in a period not covered by the Human Rights Watch report, those monitoring media freedom say there has been a sharp increase in repressing and harassing journalists, especially last month when groups of independent youths tried to demonstrate for Palestinian unity.

The Palestinian Media Forum, a journalists’ committee based in Gaza, said the central demonstration on March 15 and the subsequent rallies “were turned into a battlefield against journalists who were beaten, attacked and have had some of their equipment seized” by Hamas forces.

The Human Rights Watch study also noted that Palestinian journalists in the West Bank and in Gaza had been beaten by the Israeli military, but said it would devote a separate study to that.