"It is estimated that there are currently about 18,000 detainees held in Iraq, over 660 in Afghanistan, and about 375 at the U.S. prison in Guantanamo Bay," the American Civil Liberties Union said in a statement.

Most of those detainees "do not have access to attorneys or family members, and, under terms of the Military Commissions Act eliminating habeas corpus protections, have been denied the right to challenge their detention in civilian courts," the ACLU said.

"In addition, it has come to be known that the CIA is engaging in the unlawful practice of 'extraordinary rendition' -- the kidnapping of foreign nationals for detention and interrogation in secret overseas prisons in countries where it is known detainees are routinely tortured or abused," the human rights group said.

The Democratic-controlled 110th Congress has launched a more energetic oversight of the detainment programs in the war on terror. But the Bush administration says the current policies are essential to prevent terror groups reorganizing to carry out more deadly attacks.