WASHINGTON, June 15 - Kurdish security forces have seized scores of minority Arabs and Turkmens in the restive city of Kirkuk and secretly transferred them in violation of Iraqi law to prisons in Kurdish-controlled areas of northern Iraq, American officials said Wednesday.
The prisoners have been captured in operations by Kurdish intelligence agents and a Kurdish-led unit of the Kirkuk Police Department, sometimes with the support of American forces in the region, the officials said. The Kurds maintain broad autonomy in northern Iraq, and their intelligence agents are fiercely independent of Iraq's fledgling national intelligence service.
But American military and State Department officials condemned the transfers and said that American troops had not been involved with them, and when made aware of the practice, had sought to stop it.
"We have had serious and credible information about allegations of extrajudicial conduct, both arrests and detentions of individuals in the northern areas of Iraq," a State Department spokesman, Sean McCormack, said Wednesday at the department's daily news briefing.
"Our coalition forces, according to every report that I have, not only were not involved in these activities, but in fact raised their concerns about the fact that they had serious and credible reports that those activities were taking place."
The allegations are contained in a confidential nine-page State Department cable, dated June 5, that was first reported Wednesday by The Washington Post. Mr. McCormack confirmed the existence of the report and its major conclusions, but declined to provide any details.
Kirkuk, at the center of some of Iraq's richest oilfields, has emerged as a tinderbox for the country's major ethnic and sectarian groups, and is considered the most politically volatile city in Iraq.
Since the fall of Saddam Hussein, the Kurds have wrested control from Sunni Arabs and Turkmens of virtually every major government institution in Kirkuk, including the police. They have further consolidated their power by getting a huge turnout in the area during the elections and securing almost two-thirds of the seats in the provincial council.
Minority politicians have accused Kurdish leaders of using intimidation to exercise their authority.
About a week ago, Kurdish officials began saying the Interior Ministry in Baghdad had issued an order dismissing 2,500 Kurdish police officers in Kirkuk, telling them to return to Iraqi Kurdistan. But the Kurdish authorities balked, and Iraqi officials in Baghdad appeared to back away from their edict.
That incident reflected the power struggle between the Arab-dominated national government and the Kurd-dominated local government and police force in Kirkuk, and underscored a rift that American officials fear could intensify into broader violence in the city, which has nearly a million residents.
"The issues that we were talking about did concern the city of Kirkuk and surrounding areas in northern Iraq, and I did talk about the importance of protection of minority rights," said Mr. McCormack. "These allegations and these reports are of very serious concern to us, and we have raised our concerns in a forthright way with the authorities involved, or who we believe to be involved. There's no excuse for going outside the rule of law to try to resolve any of these pre-existing tensions."
The secret transfers of prisoners pose a potential political problem for the Bush administration, which is perceived inside Iraq to be a strong supporter of the Kurdish leaders and their political parties. Some detainees have complained they were tortured or held for months.
Just this week, President Bush telephoned the Iraqi president, Jalal Talabani, a Kurd, to congratulate him and the Kurdish people on the formation of a unified regional government.
"There's a long-simmering problem we have with the Kurds, and the embassy is working hard to address it," said an American official who has read the cable and who spoke on condition of anonymity because he was not authorized to comment.
Independent Iraq specialists said the seizures were indicative of the growing ethnic and sectarian tensions around Kirkuk.
"It's hard to know what's really going on," Joost R. Hiltermann, director of the Middle East office of the International Crisis Group, a conflict-resolution organization, said in a telephone interview from Amman, Jordan.
"The Kurds are very well organized and have security forces of their own," he said. "They arrest people, detain them and interrogate them. Some may have been involved in attacks. But the perception among minorities is that the Kurds are taking people off the street to intimidate other Arabs and extend their control."
The United States military has been aware of allegations of the secret transfers since early this year after family members complained that their relatives had been abducted, said Maj. Richard Goldenberg, a spokesman for the military's 42nd Infantry Division, which has responsibility for much of northern Iraq.
Major Goldenberg acknowledged that some prisoners had been transferred by Kurdish police or security forces to jails outside Kirkuk without proper judicial oversight, in some cases because of overcrowding in the Kirkuk jails.
But he said officers of the Idaho Army National Guard's 116th Combat Brigade, which has specific responsibility for Kirkuk, had intervened with Kurdish authorities to end the practice whenever they learned of it. American officials in Washington said they were aware of about 180 cases of secret transfers, although Sunni Arab and Turkmen politicians have said the number is much higher.
"When they observe things that are less than ideal, soldiers in units like the 116th make every effort to show Iraqis what the right model should be," Major Goldenberg said in a telephone interview from Tikrit.
He said that while American forces had worked closely with Iraqi security forces, including the Kurdish-led Emergency Services Unit, an antiterrorism squad within the Kirkuk Police Department, "the Americans did not have oversight over the judicial process once the prisoners were handed over to Kurdish authorities."
Edward Wong contributed reporting from Basra, Iraq, for this article.