One case allegedly involved an elderly Iraqi woman sodomized with a stick, according to documents obtained by the American Civil Liberties Union (ACLU).

"The documents that the ACLU has obtained tell a damning story of widespread torture reaching well beyond the walls of Abu Ghraib," the US-run prison in Iraq which has been the focus of widespread detainee abuse claims, it said.

The new allegations were discovered in Defense Department documents and other government agency records obtained via a federal court order sought by the ACLU and other groups under the Freedom of Information Act.

The other groups included the Center for Constitutional Rights, Physicians for Human Rights, Veterans for Common Sense and Veterans for Peace.

Many of the documents implicated US special forces and suggested that the Pentagon failed to aggressively investigate claims of detainee abuse even though there were "serious allegations of torture including electric shocks, forced sodomy and severe physical beatings," the ACLU said.

"Government investigations into allegations of torture and abuse have been woefully inadequate," said ACLU executive director Anthony Romero. "Some of the investigations have basically whitewashed the torture and abuse."

In one case, an "elderly Iraqi woman reported having been sodomized with a stick" while in another instance, investigators found "there was probable cause to believe" three soldiers committed the offenses of murder and conspiracy.

No action was taken against a commander believed to have been an accessory in the alleged murder and conspiracy case, where one implicated soldier was only given a written reprimand, the ACLU said.

The incident involving the woman was "closed" on the basis of a "sanitized copy" of an investigation which has yet to be released, the group said.

"These documents raise grave questions about how seriously the government is investigating allegations of torture," said Amrit Singh, a staff attorney with the ACLU Immigrants Rights Project.

In numerous cases, investigations were reportedly abandoned before relevant witnesses were questioned, the group charged.

In some investigations where guilt was found, soldiers who engaged in heinous crimes were sent back to their posts with what amounts to a slap on the wrist, the ACLU said.

In other cases, Singh said, investigations were dropped because abusive conduct was characterized as acceptable practice or as standard operating procedure.

One set of documents released by the ACLU included multiple accounts of abuse -- about 90 incidents -- at a Baghdad detainee facility called Al-Azimiyah Palace.

In sworn statements, private contractors reported having witnessed numerous instances of abuse of male and female Iraqi detainees, including forced sodomy, electric shocks, cigarette burns and beatings.

The US Justice Department has broadened its definition of torture under national and international law after human rights groups slammed a narrower definition backed by White House counsel Alberto Gonzales, now President George W. Bush's nominee to become attorney general.