Human Rights Watch (HRW) also alleged that many suspects were held in solitary confinement without being charged before they were eventually released.
The group urged George Bush, the US president, and members of the US Congress to take up the matter with Jordan's King Abdullah II and Major General Muhamad al-Dhahabi, the head of the main detention facility, both of who are currently visiting the United States.
Christoph Wilcke told reporters that the allegations, contained in a 66-page report, were based on findings from 16 cases, mostly involving Islamists. He said, however, that there were “many more cases” of such abuse.
Wilcke said most of the abusive treatment took place during the first seven days of a prisoner's detention at the country's main facility, the General Intelligence Department, in the capital of Amman.
“I have not heard of a single case where they had been able to call their family, receive visits, appoint an attorney or prepare their own defence,” he said.
“Only arrest people where they have material evidence that a crime has taken place or is about to take place.”
“This is before anybody has been sentenced to anything and should be presumed innocent,” he added.
Wilcke said that 15 out of the 16 who reported they were ill-treated during interrogation with “insults to religion or family,” sleep deprivation, and frequent beatings with bamboo sticks on the soles of their feet.
“Five minutes of beatings, then you get a rest and decide if you want to write your confession. And then another five minutes of beatings,” he said.
“There are doctors who must know about the torture that is going on. The detainees tell me that the doctor's office is right around the corner of where they are being tortured. The doctor asked them, 'Was it very bad today?” Wiicke said.
Wilcke also said the detainees told him they were confused about who interrogated them, whether it was staff at the facility or military prosecutors in charge of their cases.
Nasser Judeh, the government spokesman, said officials “will study the report seriously and respond to it through the appropriate channels.”
The Human Rights Watch researcher said Jordanian officials told him at a meeting on Monday that “there were no violations” at the facility and that they were “operating in full compliance with Jordanian law.”
He said the officials also told him that they “only arrest people where they have material evidence that a crime has taken place or is about to take place.”
But Wilke disputed the claims.
His report cited the case of Isam al-Barqawi, who was held for two years for allegedly plotting to attack the US Embassy and other targets in December 2004.
Al-Barqawi was released in June 2005 only to be arrested again a week later and held in solitary confinement ever since, the report said.
“I have not heard of a single case where they had been able to call their family, receive visits, appoint an attorney or prepare their own defence.”
HRW said the government then charged al-Barqawi with conspiracy, but more than a year later, he has yet to appear before the State Security Court or any other judicial authority.
The group urged President Bush and US congressmen to discuss the matter with Jordan's King Abdullah II and the head of the main detention facility.
Wilcke said his group recognised the dangers Jordan faced from terrorism and its need for an effective intelligence service, especially considering last November's triple hotel blasts that killed 63 people, including three Iraqi bombers.
But he urged authorities to investigate detention practices and improve the country's judicial system by giving detainees prompt access to legal counsel and the ability to challenge their detention in an independent court.