GENEVA, March 10 (Xinhua) — Two UN human rights experts said on Tuesday that they would conduct a global investigation of secret detention centers used by the United States and other countries in their counter-terrorism efforts.

The yearlong investigation is aimed not only to clarify facts, but also to ensure that such secret jails would not be used in the future, according to Manfred Nowak, UN envoy for torture, and Martin Scheinin, UN envoy for human rights and counter-terrorism.

Addressing the UN Human Rights Council, the two experts described secret jails as "one of the most horrendous practices" adopted by intelligence services.

There was "credible" evidence that the United States had transferred terror suspects for interrogation at secret detention centers in the Middle East, Eastern Europe and Asia, they said.

In many cases states receiving detainees had "reportedly engaged in torture and other forms of ill-treatment," they said.

Scheinin welcomed U.S. President Barack Obama’s decision to close the Guantanamo Bay detention center, but he said scrutiny of the U.S. counter-terrorism policy would not be relaxed.

"We will not let the United States off the hook simply because of the change in administration," he said.

He also stressed those investigations of abuses at the Guantanamo Bay prison should continue until everything was revealed.