The top U.N. human rights official on Friday denounced the use of secret detention centers in the war on terrorism, and said governments must treat prisoners according to the law, avoiding torture and providing fair trials.

Louise Arbour, in a speech to the new U.N. Human Rights Council, was clearly referring to repeated allegations of U.S. abuses.

"It is vital that at all times governments anchor in law their response to terrorism," said Arbour, U.N. high commissioner for human rights.

The U.S. delegation responded that it was U.S. policy to treat captured combatants humanely.

Ambassador Warren W. Tichenor, who heads the U.S. delegation to the 47-nation council, said the United States adhered to its "absolute commitment to uphold our national and international obligations to eradicate torture and to prevent cruel, inhuman or degrading treatment or punishment worldwide."

Arbour said that "the reported existence of secret detention centers where suspects are held incommunicado is ... of grave concern."

"Such practices also have a corrosive effect on the rule of law and human rights, and create an environment ripe for other abusive conduct," she said.

While the magnitude of terrorist threats had raised questions about whether the existing legal framework should yield to a new reality, Arbour said, governments must continue to abide by international law, which includes an absolute ban on torture and the right to a fair trial.

The United States has been widely criticized for detaining hundreds of terror suspects at Guantanamo Bay, Cuba, for years without charging them or providing them with access to courts.

Governments are also bound by the international prohibition against sending individuals back to a country where they face the risk of torture, Arbour said, referring to another allegation lodged against the U.S.

"In addition to not engaging in acts of torture themselves, states have a positive obligation to protect individuals from exposure to torture," she said.

There should be no exceptions, even to fight terrorism, she said. "Torture delegitimizes state action to the point where the state can no longer assert its moral authority."

European investigators and human rights groups, following on a report that first appeared in The Washington Post in November, have said European nations let the CIA abduct and transport terror suspects to secret detention facilities in Europe and to locations elsewhere where they might have faced torture.

Clandestine prisons and secret flights to countries where suspects could face torture would breach the Europe's human rights treaties, including the European Convention on Human Rights.

Arbour urged all countries to disclose and prosecute any alleged abuses of human rights in the fight against terrorism.

"To disregard the law or to carve out improper exceptions, as has been attempted by many governments, would lead to a steady erosion of fundamental rights and, ultimately, undermine the legitimacy of government action itself," she said.