Mehdi Ghezali said he had been tortured by exposure to freezing cold, noise and bright lights and chained during his 30-month imprisonment.
Ghezali, the son of an Algerian-born immigrant, told Swedish media in interviews published or aired on Wednesday that he was interrogated almost every day at the US naval base on Cuban soil.
The 25-year-old man, who was arrested in Pakistan where he
says he was studying Islam, was released on 8 July after
pressure from Sweden.
Ghezali told Dagens Nyheter daily and Swedish public radio he had cooperated for the first six months but stopped talking when his interrogators kept asking the same questions.
In April the military changed their tactics, he said.
"They put me in the interrogation room and used it as a refrigerator. They set the temperature to minus degrees so it was terribly cold and one had to freeze there for many hours - 12 to 14 hours one had to sit there, chained," he said, adding that he had partially lost the feeling in one foot since then.
Ghezali said he was also deprived of sleep, chained for long periods in painful positions, and exposed to bright flashes of light in a darkened room and loud music and noise.
"They forced me down with chained feet. Then they took away the chains from the hands, pulled the arms under the legs and chained them hard again. I could not move," he said.
After several hours his feet were swollen and his whole body was aching. "The worst was in the back and the legs," he said.
Ghezali said he went to Pakistan to study Islam in August 2001, before the September 11 attacks which triggered President George Bush's War on Terrorism and the US-led invasion of Afghanistan.
He said he was visiting a friend in the Afghan town of Jalalabad near the Pakistani border when the US invasion started. He decided to return to Pakistan when he heard that villagers were selling foreigners to US forces.
Pakistani villagers seized him as he crossed the border from Afghanistan and sold him to Pakistani police, who turned him over to the US military. He was flown from Pakistan to Afghanistan and arrived in Guantanamo Bay in January 2002, he said.
He was released from Guantanamo on 8 July because he was no longer considered a threat to the United States.