The United States has not announced formally it is detaining anyone without trial, but since 11 September more than 1,100 people have been arrested in the anti-terrorism sweep.
A large proportion of them are foreign nationals being held on immigration violations or petty crimes that would not ordinarily warrant detention.
Last week, the Justice Department put the number of detainees at 1,183 and said it would in future no longer give the numbers.
Civil liberties activists have accused the Attorney General, John Ashcroft, of holding people under secretive conditions on the flimsiest of pretexts in violation of the usual standards of due process.
Only a dozen of the detainees are believed to be of interest to investigators seeking to root out cells connected to al-Qa'ida, and of these only five are suspected of direct links to the terrorist attacks. None has been charged. Of the others, many appear to have been denied access to lawyers. Even information on their whereabouts has not been forthcoming. Court hearings have been held in secret.
Anti-terrorism legislation passed last month lets Mr Ashcroft hold a non-citizen on an immigration violation indefinitely. Mr Ashcroft has also issued an order empowering the FBI to eavesdrop on conversations between certain detainees and their lawyers. America argues, as Britain does, that the exceptional threat to national security justifies these restrictive measures.