The United States comes under official U.N. grilling for the first time Friday over its compliance with the global ban on torture, with questions focusing on allegations of secret CIA prisons and flights transferring terror suspects for possible torture in other countries.

The U.N. Committee Aganist Torture, the global body's watchdog for a 22-year-old treaty forbidding prisoner abuse, will quiz U.S. officials on a series of issues ranging from Washington's interpretation of the absolute ban on torture to its interrogation methods in prisons such as Abu Ghraib and Guantanamo Bay.

The United States, like the 140 other nations that have signed the Convention Against Torture, must submit reports to the committee to show it is applying the rules.

The U.S. mission to the U.N.'s European headquarters in Geneva said it has sent a written reply to the committee's questions, but that it would refrain from commenting ahead of its sessions with the committee on Friday and Monday. Its team of 25 for the hearings will be headed by State Department legal adviser John B. Bellinger III, and includes officials from the Defense, Justice and Homeland Security departments.

In its 87-page report filed in January — some four years behind schedule — Washington insisted it is "unequivocally opposed" to torture and that its commitment to the ban "remains unchanged" since the U.S. Senate ratified the convention in October 1994.

But the Geneva-based committee, a panel of 10 independent experts who meet twice a year, said the United States' legal interpretation of torture in Department of Justice memorandums in 2002 and 2004 "seems to be much more restrictive than previous United Nations standards."

The committee is demanding the United States explain why it established secret prisons, what rules and methods of interrogation it employs, and whether the administration of U.S. President George W. Bush assumes responsibility for alleged acts of torture committed by American agents outside U.S. territory.

"In view of the numerous allegations of torture and ill-treatment of persons in detention under the jurisdiction of (the United States) and the case of the Abu Ghraib prison, what specific measures have been taken to identify and remedy problems in the command and operation of those detention facilities?" the committee has asked.

It has also questioned more specifically whether there has been any "independent investigation regarding the possible responsibility of the high-ranking officials of the administration, including the CIA, the Department of Defense, the Department of Justice and the armed forces, for authorizing or consenting in any way" to acts of torture.

Criticism by the U.N. panel brings no penalties beyond international scrutiny. The committee is expected to issue conclusions when it wraps up its session May 19.

Washington's report said President Bush "has made clear that the United States stands against and will not tolerate torture under any circumstances."

It noted that it has a separate system of military justice for its armed forces personnel, which is responsible for handling claims of abuse from detainees in Afghanistan, Iraq and Guantanamo Bay. Allegations concerning CIA activities are currently under review by the agency's Inspector General, the report said.

"When allegations of abuses arise, they in all cases will be investigated and, if substantiated, prosecuted," the report said.

Washington neither confirms nor denies allegations of secret prisons on grounds that it refuses to comment on intelligence matters.

But the committee cautioned that enforced disappearances of suspects "can be considered a form of torture" and asked for details on the U.S. policy of "rendition."

U.S. officials have acknowledged flying up to 150 of the most serious terror suspects from one country to another, but said they receive "diplomatic assurances" from authorities that they won't use torture on the detainees they receive.

But rights groups say some have been tortured anyway and that the United States is violating the treaty in other ways.

"There are certain things that are not permissible no matter what," said Jennifer Daskal, who heads Human Rights Watch's U.S. advocacy program. "Torture is one of those things, and there is no justification for torture."