US detained scores of Muslims after Sept 11

The men were held behind a veil of secrecy under a US law permitting the arrest and detention of "material witnesses" thought to have important information about a crime and considered likely to flee, the groups said.

"A handful" were later charged with crimes related to terrorism. About half were never brought to testify, and the US government apologised to 13 of the men for wrongfully detaining them, according to the 101-page report.

"Muslim men were arrested for little more than attending the same mosque as a September 11 hijacker or owning a box-cutter," said Anjana Malhotra, a researcher at Human Rights Watch and the American Civil Liberties Union.

The US Justice Department has declined to reveal how many material witnesses it jailed in its counterterrorism investigations, but Human Rights Watch and the ACLU said they had confirmed 70 such detentions after a year of research.

Sixty-four were of Middle Eastern or South Asian descent, 17 were US citizens, and all but one was Muslim, a statement accompanying the report said.

"The Justice Department relied on false, flimsy or irrelevant evidence to secure arrest warrants for the men," almost all of whom had cooperated with authorities prior to their detention, it said.

The men were typically taken at gunpoint, held in solitary confinement, harassed and in some cases physically abused, the groups said.

Court documents were sealed, court proceedings were held behind closed doors, and the men were largely denied legal protection guaranteed by US law, they charged.

One-third were held at least two months, some were held six months and one man spent more than a year behind bars.

"Many were not informed of the reason for their arrest, allowed immediate access to a lawyer, nor permitted to see the evidence used against them," the statement said.