GENEVA - Two United Nations special rapporteurs said Tuesday they would investigate secret detention centres used by the CIA in counter-terrorism efforts.

"We call on all governments to cooperate, not just in clarifying the facts, but in ensuring that such secret detention centres will no longer be used in the future," Manfred Nowak, the UN Special Rapporteur on Torture said.

Nowak and Martin Scheinin, Special Rapporteur on Human Rights and Counter-terrorism will study locations alleged to have hosted such secret detention centres, including US military bases.

Besides secret jails run by the CIA, the study would also probe alleged prisons run by other governments.

Scheinin said such prisons were "one of the most horrendous practices" that emerged after the September 11 attacks in the US, while Nowak hoped that this "will stop, and perhaps is in the process of being stopped."

The results of the probe should be ready in a year.

The two independent experts mandated by the UN Human Rights Council hailed US President Barack Obama's decision to close the Guantanamo prison and all CIA prisons operating abroad.

Nowak said he was also "very encouraged" by the fact that Warsaw is probing allegations of a secret CIA jail near Szymany in northeast Poland.

Besides alleged detention centres in Poland and Romania, the two experts will look into the role played by over 10 American military bases in the world, which have been alleged to have also sheltered secret jails.

"We are fully aware" of the problem, said Nowak, citing the military base of Tuzla in Bosnia, which was suspected of having served as a temporary holding centre for detainees before their transfer to Guantanamo.