Geneva ? The top U.N. human rights official expressed concerns Friday about reports of secret detention centers for terrorist suspects, warning governments to abide by the law or risk creating an environment ripe for abuses.

European investigators and human rights groups have accused European nations of letting the CIA abduct and transport terror suspects to secret detention facilities where they might have faced torture. Governments largely have denied the accusations.

“The reported existence of secret detention centers where suspects are held incommunicado is : of grave concern,” U.N. High Commissioner for Human Rights Louise Arbour said in a clear reference to the allegations of U.S. abuses. She did not, however, specifically name the United States.