"There is widespread agreement that the political environment has become increasingly abusive and defined by force," HRW said in a 73-page report based on interviews with former political prisoners.

The report, Like the Dead in Their Coffins: Torture, Detention, and the Crushing of Dissent in Iran, echoed the pessimism of Iran's reformist president, Mohammad Khatami, who has all but conceded defeat in his struggle with hardliners.

Mr Khatami's calls for expanding democratic rights were applauded by many Iranians, but denounced by hardliners as a betrayal of the 1979 Islamic revolution which toppled the shah and brought clerics to power.

Iran's judiciary is seen as firmly in the hands of hardliners who are led by the supreme leader, Ayatollah Ali Khamenei.

HRW said the judiciary was "at the centre of the human rights violations" documented in its report.

During his first four-year term, Mr Khatami relaxed some of the country's strict Islamic laws and allow greater media freedoms.

By the time of his second-term victory in 2001, hardliners were fighting back, shutting down more than 100 liberal publications and detaining dozens of activists and writers.

"The Iranian authorities have managed, in the span of four years, to virtually silence the political opposition within the country through the systematic use of indefinite solitary confinement of political prisoners, physical torture of student activists and denial of basic due process rights..." HRW said.

Asked yesterday about human rights violations, a spokesman for the judiciary said torture had decreased significantly in Iran since April when the judiciary chief, Ayatollah Mahmoud Hashemi Shahroudi, ordered a ban on the use of torture to obtain confessions. The ban was seen as the first public acknowledgment of the practice in the country.

Describing the future as "bleak", HRW said: "The authorities have largely succeeded in their campaign to send a message to the public that the costs of voicing peaceful political criticism are unbearably high."