At least six of those currently detained are reported to have been assaulted and denied medical treatment. One detainee who appeared in court today told the magistrate that he had been beaten on the head with a truncheon and punched all over his body.

'There has been an alarming pattern of Malaysian police brutality against reformasi (pro-reform) demonstrators. This raises serious concerns that today's decision to detain leading members of an opposition party for a further six days will leave them vulnerable to abuse,' Amnesty International said.

The demonstrators were among supporters of former Deputy Prime Minister and prisoner of conscience Anwar Ibrahim who took to the streets last Saturday to mark the first anniversary of his prison sentence. The Malaysian Police Act outlaws unauthorized gatherings of more than three people and provides for a prison sentence of up to one year.

Since 1998, more than 1,200 people have been arrested in unprecedented public demonstrations in support of Anwar Ibrahim's arrest. Many of those arrested were assaulted in custody and face trials this year for illegal assembly.

Amnesty International is calling on the Malaysian government to release those who have been detained solely for exercising their right to engage in peaceful assembly, to ensure those who have been detained have access to lawyers, family and medical attention, and to investigate all allegations of police ill-treatment in custody.