The parliamentary assembly of the 55-nation OSCE in Rotterdam adopted a resolution that urged the United States to immediately present the prisoners before a competent tribunal to have their status determined.
It asked the US to secure the prisoners' rights by letting them be represented by legal council of their own choice and to refrain from the use of the death penalty.
The OSCE resolution follows close on the heels of a similar demand by the Council of Europe, a pan-European rights watchdog. At a meeting on June 26, it condemned the US for holding the Guantanamo Bay prisoners in unacceptable conditions and disregarding recognised legal standards.
The detention by the US of more than 600 combatants and non-combatants at Guantanamo Bay and in Afghanistan is unlawful -- since their status is undefined in international law -- and their conditions of detention are unacceptable, the Council assembly had said in a statement.
Meanwhile, Britain's Tony Blair on Wednesday said his government was pressing Washington behind the scenes to ensure the planned trials of the Guantanamo suspects did not violate international law.
Under repeated questioning in the United Kingdom Parliament, Blair declined to condemn the trials or call for the extradition of Britons in Guantanamo, leaving their relatives and lawyers frustrated.
Christian (R): US move
against all norms
Louise Christian, a lawyer for UK Guantanamo Bay prisoner Feroz Abbasi's family said that despite being the US’ closest ally if Britain was unable to do anything for its citizens held in Guantanamo, it would be a disgrace.
The US plans for military trials of a first batch of six foreigners -- including two Britons -- at the naval base in Cuba, have provoked worldwide criticism and strained the close US-UK political alliance. The trials could end in the death penalty.
The detainees at Guantanamo -- who were alleged to have links with the al-Qaeda network and Afghanistan's former Taliban government -- are deprived of prisoner-of- war status and kept in the open air at the base.
The conditions in which the prisoners are being held and the US' disregard for their rights have raised outcry from the United Nations, Britain, rights groups and lawyers.
Pakistani and Afghan prisoners released from Guantananmo have complained of harsh treatment. One said detainees had been tortured by US guards and those still imprisoned at Guantanamo had become mentally deranged.