Hamas backed the Guardian's findings on Friday during a press conference, and blamed Keith Dayton, the US General commanding the Palestinian National Security Force in the West Bank, for the arrest and torture of its supporters.

Hamas called on Barack Obama, the US president, to remove Dayton from his position and said Mahmoud Abbas, the Palestinian president and Fatah leader in the West Bank, was responsible for the "crimes" against Hamas in the West Bank.

Human rights organisations say it is common for detainees to be badly beaten and subjected to "shabeh", where they are shackled and held in painful positions for long periods.

Hamas, which has de facto control of the Gaza Strip, has faced allegations that its own forces have detained and tortured people allied with Fatah, a rival Palestinian group that is a member of the Palestinian Authority.

Hundreds held

Between 400 and 500 Hamas supporters are currently being held by the PSF and GI, officials from the PA have said.

But Adnan Aldenari, a Palestinian police spokesman, denied that the security forces in the West Bank were abusing detainees.

"We have nothing to hide; or nothing to be ashamed of. When we had mistakes [they] were individual as committed by some officers and not expressive of our policy.

"The CIA ... only supports, and is interested in, lawful methods that produce sound intelligence."

Paul Gimigliano,
CIA spokesman

"Our prisons and detention facilities are open and not secret as they are in some other countries. They are open to the media and human rights organisations."

The Guardian reported that at least three detainees have died in custody this year due to being mistreated.

The most recent was Haitham Amr, a 33-year-old nurse from Hebron, who died four days after he was detained by GI officials last June, the newspaper said.

Shawan Jabarin, the general director of al-Haq, a Palestinian human rights organisation, told the Guardian: "The Americans could stop it any time. All they would have to do is go to [prime minister] Salam Fayyad and tell him they were making it an issue.

"Then they could deal with the specifics: they could tell him that detainees needed to be brought promptly before the courts."

A regional diplomat told the newspaper that "at the very least" US intelligence officers were aware of the torture and were not doing enough to stop it.

The CIA does not deny working with the PSF and GI in the West Bank, but Paul Gimigliano, a CIA spokesman, said that the US agency does not hold a supervisory role.

"The notion that this agency somehow runs other intelligence services ... is simply wrong," he told the Guardian.

"The CIA ... only supports, and is interested in, lawful methods that produce sound intelligence."