Senior U.S. military commanders in Iraq have known since early this year of reports that Iraqi security forces had physically abused detainees, according to Pentagon documents.

The first widely reported abuse case came to light when U.S. and Iraqi forces discovered 173 malnourished Iraqi detainees at an Interior Ministry bunker in Baghdad on Nov. 13. Some inmates reportedly showed signs of torture, and a U.S. general was so concerned that he took immediate control of the facility.

More than five months earlier, Gen. George Casey, the top U.S. commander in Iraq, wrote a policy memorandum on the importance of Iraqi security forces being trained to respect the rule of law and basic human rights.

"Over the past several months I have received reports of serious physical abuse of detainees by ISF," he wrote on June 22, using the acronym for the Iraqi security forces.

In the memo, obtained Wednesday by The Associated Press, he said he forwarded the reports to Iraqi government officials. He did not elaborate in his memo on specifics of the reported physical abuses.

"Abuse of detainees by ISF is a violation of Iraqi law and counterproductive to all of our intended efforts here," Casey wrote.

A joint U.S.-Iraqi investigation is now under way to check conditions at Iraqi-run detention facilities.

In addition, Defense Secretary Donald H. Rumsfeld has asked military commanders to clarify the circumstances under which American troops are obliged to intervene to stop any Iraqi abuses they witness. However, Rumsfeld has not indicated publicly that he knew of reports of Iraqi abuse dating back to early this year.

Nine days after the Casey memo, in a satellite video news conference from Iraq, Maj. Gen. David Rodriguez told reporters at the Pentagon that he had received about 40 reports of abuse by Iraqi security forces in the previous six or eight weeks in the northwest section of Iraq in which his troops operate. He said Iraqi officials had investigated several cases and had "taken appropriate action" against those found to be responsible.

He said the reported abuses were not life threatening.

"Wherever we see a human rights violation and people doing the wrong thing, we intervene immediately to stop the misuse of detainees or prisoners," Rodriguez said.

His area of responsibility does not include Baghdad.

In recent remarks on the issue of Iraqi abuse of detainees, Rumsfeld has stressed his interest in clarifying the rules governing the response of American troops. When Gen. Peter Pace, the chairman of the Joint Chiefs of Staff, told reporters Nov. 29 that all U.S. service members are obliged to intervene to stop inhumane treatment they see, Rumsfeld said, "I don't think you mean they have an obligation to physically stop it; it's to report it."

No, Pace said, they are supposed to stop it.

Since then, Rumsfeld has asked that these rules be clarified. He alluded to the matter in a speech on Monday, citing the danger of a host country taking legal action against U.S. troops who use force to stop detainee abuses.

"And so reporting something that looks amiss is good," Rumsfeld said. "Orally trying to stop something that looks amiss, to me, sounds very reasonable. And then the next question is: What level of force should they use to try to stop it if they see it happening in a country where they don't know the laws."

In his June 22 memo, Casey wrote that U.S. troops are obliged to "take all reasonable action" in accordance with military rules to stop or prevent any observed or suspected instances of physical or mental abuse that are "likely to lead to serious injury or the death of detained persons in Iraqi custody," and to promptly report it.

A Rumsfeld spokesman, Bryan Whitman, said Wednesday that Rumsfeld wants a clearer definition of "all reasonable action."