According to the UN group, almost all those it interviewed said they were tortured or mistreated in Malaysia’s detention centres.
Malaysia says it is amending the laws, but has not yet said how.
The UN Working Group on Arbitrary Detention spent a week visiting prisons and detention centres.
It reported that between 2003 and 2007, over 1,500 people died while being held by authorities.
Of the detainees it interviewed, almost all complained of beatings, being confined in small spaces without light and having dirty water thrown on them.
That is in stark contrast to the country’s prisons, where there were no allegations of abuse, says the BBC’s Jennifer Pak in Kuala Lumpur.
Mr Malick Sow, who led the UN working group, said people preferred being in prison rather than police stations and immigration detention centres, because they felt safer there.
He said much of the abuse happened in the initial period of detention when detainees are not allowed to contact their lawyer or family.
He said the problem was more acute under the country’s preventive laws including the Internal Security Act, which allows for detention without trial for up to 60 days with the possibility of extensions for years.
The law has been used in the past against politicians and journalists.
Those held under the Act have no access to judicial appeal.
However, fewer people have been held under the law in recent years and the Malaysian government is expected to table amendments to address some of the issues next month.