Human rights groups and lawyers in the United States have criticised the decision to use special military commissions to try six men accused of organising the September 11 terrorist attacks.

Secretary of Homeland Security Michael Chertoff has promised a fair trial for the defendants who are being held at Guantanamo Bay detention camp.

Lawyers from the Centre for Constitutional Rights are representing one of the defendants.

Organisation executive director Vincent Warren says the six men should be tried in criminal courts.

"With respect to the rights that the general is saying the detainees have, it's really problematic on a number of levels," he said.

"First of all, while they may have a right to remain silent in this process, they didn't have the right to remain silent when they were being waterboarded over a period of time and held in CIA facilities."