This is the Cuban government's first attack on the use of the facility to hold men Washington has seized in its "war on terror".
"In the territory illegally occupied by the Guantanamo naval base, hundreds of foreign prisoners are subjected to indescribable abuses," said a statement passed by parliament earlier this week and broadcast by the state-run media in Havana on Friday.
Communist-run Cuba's National Assembly said prisoners were isolated and denied the right to communicate with their families or to prepare an adequate defence.
"Some of the few freed have spoken of the horrors of this concentration camp," said the statement, appealing to lawmakers throughout the Americas to halt US human rights violations.
President Fidel Castro's government surprised observers when after the 11 September attacks it offered logistical support to Washington as it transformed the base at Guantanamo into a prison for suspected Taliban soldiers from Afghanistan.
"Some of the few freed have spoken of the horrors of this concentration camp"
Since Castro came to power in a 1959 revolution the US naval base at Guantanamo Bay has been a flashpoint of hostilities between the two countries.
Castro insists the area is illegally occupied by the US which leases it under a pre-revolution agreement.
The Cuban president refuses to cash US checks for use of the base, which he keeps in a desk drawer to show visitors and reporters.
To date Havana has refrained from criticising Washington's use of the naval base even as international unease with conditions there mounts.
The US has kept more than 600 people from several countries captive for nearly two years at Guantanamo following the undeclared war against the Taliban government in Afghanistan and al-Qaida.
Earlier in December, a US appeals court ruled that they cannot be held indefinitely and cannot be denied lawyers.