KABUL, Afghanistan — Detainees are hung by their hands and beaten with cables, and in some cases their genitals are twisted until the prisoners lose consciousness at sites run by the Afghan intelligence service and the Afghan National Police, according to a United Nations report released here on Monday.

The report, based on interviews over the past year with more than 300 suspects linked to the insurgency, is the most comprehensive look at the Afghan detention system and an issue that has long concerned Western officials and human rights groups.

It paints a devastating picture of abuse, citing evidence of “systematic torture” during interrogations by Afghan intelligence and police officials even as American and other Western backers provide training and pay for nearly the entire budget of the Afghan ministries running the detention centers.

The report does not assess whether American officials knew of the abuses. But such widespread use of torture in a detention system supported by American mentors and money raises serious questions about potential complicity of American officials and whether they benefited from information obtained from suspects who had been tortured.