U.S. authorities deliberately trampled constitutional rights after Sept. 11 in a crackdown that saw immigrants jailed without cause, tried in secret and, in some cases, physically abused, a leading human-rights group has charged.

In a report to be released today, Human Rights Watch accuses President George W. Bush's government of displaying "a stunning disregard for the democratic principles of public transparency and accountability" in its response to the terrorist attacks on New York and Washington.

It says authorities rounded up at least 1,200 people because of their religion or ethnic background, jailed them on immigration charges to deny them rights normally enjoyed by accused persons, and held many in harsh isolation conditions.

In court documents or interviews with the group's researchers, several detainees said they were beaten by interrogators or by fellow inmates acting with apparent impunity, the report says. Others told of humiliating treatment and verbal abuse.

The 99-page report, titled Presumption of Guilt, says the government has violated the same principles of freedom that Mr. Bush said were attacked by hijackers who flew airplanes into the World Trade Center and Pentagon.

"The country has witnessed a persistent, deliberate and unwarranted erosion of basic rights against abusive governmental power," it adds.

Despite the massive dragnet that mainly targeted Muslim, South Asian and Middle Eastern men, none of those detained after Sept. 11 has been charged with a terrorism-related offence.

The report says it is difficult to document cases of physical abuse because there is little independent access to detainees.

But it cites a Roman Catholic citizen of the Ivory Coast, Tony Oulai, who told a Human Rights Watch researcher he was repeatedly beaten on Sept. 17 in a Florida detention centre to the point where he was "begging for my life" and bleeding from the nose, mouth and ears.

A Pakistan-born, legal U.S. resident charged with larceny, Qaiser Rafiq, told the group he was beaten three times by inmates in a Connecticut jail after a local newspaper article said he was suspected of involvement in terrorism. Guards saw the beatings but took no action, he said.

Human Rights Watch, a private New York-based monitor of rights guaranteed in domestic and international law, called on authorities to release the names of all detainees and to stop targeting suspects solely because of racial origin.

The group's U.S. advocacy director, Wendy Patten, said in an interview that authorities used immigration charges to make an "end run" around the safeguards and court scrutiny ensured in criminal cases.

By holding suspects on immigration charges, authorities avoided having to give reasons for arresting suspects, bring them before a judge within 48 hours and provide court-appointed lawyers.

According to government figures, 752 of those detained in the United States after Sept. 11 were eventually charged with immigration violations and most of those have been deported. But some spent weeks in jail before being freed.

The report takes a shot at the official contention that revealing the names of detainees would allow terrorist groups to chart the progress of investigations. Any illegal group would find out quickly if one of its members were arrested, it says, also noting that U.S. authorities freely provided information to the embassies of countries whose citizens were arrested.