GENEVA, June 25: United Nations human rights investigators on Friday demanded access to prisoners held by US forces in Iraq, Afghanistan and Guantanamo Bay to check that international standards were being upheld.

In a rare joint statement, they unequivocally condemned terrorism in all forms, but reiterated "concerns about certain measures taken in the name of the fight against terrorism".

The US military, facing a backlash across the Arab world for its abuse of Iraqi prisoners, last month launched an investigation into its treatment of detainees in Afghanistan - the first stop in United States President George Bush's "war on terror".

The UN statement said a panel of rapporteurs spanning areas such as torture and arbitrary detention should visit inmates held for suspected terrorism offences in Iraq, Afghanistan, the military base at Cuba's Guantanamo Bay, and elsewhere.

"This is a collective step in the hope that it will have more effect," Theo van Boven, U.N. special rapporteur on torture, told a news conference after chairing closed-door talks with 30 rights investigators.

The plea follows a scandal last month sparked by photographs taken in the US-run Abu Ghraib jail in Iraq, showing prisoners, some in hoods, being humiliated by soldiers and intimidated with dogs.

On the subject of Abu Ghraib, Van Boven said: "The whole picture being drawn up is a matter of great concern."

He said a 1987 Convention against Torture - ratified by the United States - was clear. "The prohibition of torture and inhuman and degrading treatment is an absolute one. It may not be derogated from in any circumstances."

Mr Bush said this week that he had never ordered and would never order detainees to be tortured.

Reed Brody, counsel at the New York-based Human Rights Watch, said: "If the Bush administration is serious about its rejection of torture, it needs to let UN inspectors in."

Activists have expressed alarm that many people arrested since the Sept 11, 2001, attacks in the United States have been held for more than two years without charges being laid, often incommunicado, which can facilitate mistreatment.

Van Boven said he wanted to investigate suspected abuses in more than 10 countries - including China and Russia - but that the United States had a special role.

"There is a tendency among many other countries, particularly those where the United States has influence, to say if the US can afford to do that, why should we not follow suit?," he said.-Reuters