Iran's hard-line conservative rulers have succeeded in stifling public criticism through illegal arrests, systematic beatings and "white torture" in secret prisons, according to a new report by an international watchdog group.

Human Rights Watch, a New York-based advocacy group, concluded that hard-liners have intimidated critics by shuttering dozens of newspapers, arresting student protesters by the thousands and operating jail facilities beyond the reach of Iran's elected reformers. "White torture" is the term political prisoners use for excruciating confinement alone inside tiny, artificially lit cells for weeks at a time.

The title of the 65-page report, "Like the Dead in Their Coffins: Torture, Detention and the Crushing of Dissent in Iran," refers to the rows of solitary cells in which detainees were confined. The cells typically measure 3 feet by 6 feet.

Massoud Behnoud, a journalist who eventually fled overseas, is quoted in the report as saying, "In the first few hours it is very hard. You have never been so close to walls in your life."

The report details the "climate of fear" noted in a U.N. human rights report issued in January. The U.N. report mentioned a downward trend for human rights in Iran that diplomats and other observers trace to 2000, when political reformers swept into parliament with promises to ease the grip of religious conservatives on daily life and reform a corrupt economy.

The reformists' electoral victory provoked hard-liners to fight back by using the appointive offices that remained under the control of Ayatollah Ali Khamenei, the supreme authority in Iran's theocracy. This year, one appointed body, the Guardian Council, was widely condemned for disqualifying about 2,400 reform candidates from parliamentary elections in February, ensuring a conservative victory. Gholam Ali Haddad Adel, whose son is married to Khamenei's daughter, was elected parliamentary speaker on Sunday.

The human rights report also documented a parallel, four-year effort by Iran's conservative judiciary to stifle the public discussion that fueled the reform movement.

"By targeting the leadership of the student activist community and the most influential writers and newspaper editors, the government was able to chill expression among the larger public," the report stated.

Students were more likely than journalists to suffer beatings in prisons controlled by the judiciary or Revolutionary Guard Corps, the report said, noting that more than 4,000 were rounded up by plainclothes agents in demonstrations last July.

Last July , a Canadian photographer, Zahra Kazemi, died after being beaten into a coma during interrogation in a Tehran prison two weeks before. Canada recalled its ambassador over the incident.