"While a handful of countries received persons rendered by the United States during this period, no other country is believed to have held as many as Jordan," the rights group said in a statement.
The prisoners were interrogated and tortured by Jordan's General Intelligence Department, according to a new Human Rights Watch report that documents eight previously unknown cases of rendition.
GID officials who met with Human Rights Watch in Amman in 2007 denied receiving CIA prisoners and denied using torture. The group said the denials were unconvincing "given the weight of credible evidence showing otherwise."
The report is "based largely on firsthand information from Jordanian former prisoners who were detained with the non-Jordanian terrorism suspects," it said.
"We've documented more than a dozen cases in which prisoners were sent to Jordan for torture," said Joanne Mariner, terrorism and counterterrorism director at Human Rights Watch.
Prisoners rendered to Jordan included at least five Yemenis, three Algerians, two Saudis, a Mauritanian, a Syrian, a Tunisian, and one or more Chechens from Russia, the group said.
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They may also have included a Libyan, an Iraqi Kurd, a Kuwaiti, one or more Egyptians, and a national of the United Arab Emirates.
The report includes an excerpt of a note handwritten by a rendered prisoner while in Jordanian custody in late 2002. The prisoner is now at the US war on terror prison camp at Guantanamo Bay, Cuba.
Ali al-Hajj al-Sharqawi wrote that GID interrogators beat him "in a way that does not know any limits."
"They threatened me with electricity, with snakes and dogs .... [They said] we'll make you see death .... They threatened to rape me," the note said.
A common torture method was falaqa, by which prisoners are given extended beatings on the bottoms of their feet.
"Just about everyone at GID was beaten with sticks," a Jordanian former prisoner told Human Rights Watch. "People were beaten on their feet. They did it in the basement."
"Outsourcing torture is not only wrong, it's illegal," Mariner said. "And the US can't say it doesn't torture if it sends people to countries that do."
© 2008 Agence France Presse