The report shows little progress in curbing abuse in Afghan prisons despite a year of effort by the U.N. and international military forces in Afghanistan. The report also cites instances where Afghan authorities have tried to hide mistreatment from U.N. monitors.

The slow progress on prison reform has prompted NATO forces to once again stop many transfers of detainees to Afghan authorities out of concern that they would be tortured.

In multiple detention centers, Afghan authorities leave detainees hanging from the ceiling by their wrists, beat them with cables and wooden sticks, administer electric shocks, twist their genitals and threaten to shove bottles up their anuses or to kill them, the report said.

In a letter responding to the latest report, the Afghan government said that its internal monitoring committee found that “the allegations of torture of detainees were untrue and thus disproved.” The Afghan government said that it would not completely rule out the possibility of torture at its detention facilities, but that it was nowhere near the levels described in the report and that it was checking on reports of abuse.

The findings, however, highlight the type of human rights abuses that many activists worry could become more prevalent in Afghanistan as international forces draw down and the country’s Western allies become less watchful over a government that so far has taken few concrete actions to reform the system.

As one detainee in the western province of Farah told the U.N. team: “They laid me on the ground. One of them sat on my feet and another one sat on my head, and the third one took a pipe and started beating me with it. They were beating me for some time like one hour and were frequently telling me that, ‘You are with Taliban and this is what you deserve.’”

More than half of the 635 detainees interviewed had been tortured, according to the report titled Treatment of Conflict-Related Detainees in Afghan Custody: One Year On. That is about the same ratio the U.N. found in its first report in 2011.

It’s a troubling finding given the amount of international attention and pledges of reform that came after the first report. At that time, the NATO military alliance temporarily stopped transferring Afghans it had picked up to national authorities until they could set up a system free of abuse. Though it said the findings were exaggerated, the Afghan government promised after the first report to increase monitoring.

But little appears to have changed. Once NATO forces resumed the transfers and decreased inspections, torture quickly returned to earlier levels, the report said. And even though the international military force was making a serious effort to delay transfers if there was risk of torture, about 30 percent of 79 detainees who had been transferred to Afghan custody by foreign governments ended up being tortured, the report said. That’s higher than in 2011, when the U.N. found that 24 percent of transferred detainees were tortured.

“Torture cannot be addressed by training, inspections and directives alone,” said Georgette Gagnon, the head of human rights for the U.N. mission in Afghanistan, explaining that there has been little follow-through by the Afghan government.

In particular, the U.N. report found that the Afghan government appeared to be trying to hide the mistreatment and refusing to prosecute those accused of torturing prisoners.

The U.N. team received “multiple credible reports” that in some places detainees were hidden from international observers in secret locations underground or separate from the main facility being inspected. Also, the observers said they saw what appeared to be a suspicious increase in detainees held at police facilities when an intelligence service facility nearby was being monitored.

And particularly in the southern province of Kandahar, the U.N. received reports that authorities were using unofficial sites to torture detainees before transporting them to the regular prison.

In a letter responding to the U.N. report, Gen. John Allen, the commander of U.S. and NATO forces in Afghanistan, said that his staff had written letters to Afghan ministers urging them to investigate more than 80 separate allegations of detainee abuse during the past 18 months.

“To date, Afghan officials have acted in only one instance,” Allen said in the letter. In that case Afghan authorities did not fire the official in question, but transferred him from Kandahar province to Sar-e-Pul in the north.

The report documents what it called a “persistent lack of accountability for perpetrators of torture,” noting that no one has been prosecuted for prisoner abuse since the first report was released.

Aimal Faizi, a spokesman for the Afghan president, said torture and abuse of prisoners was not Afghan policy.

“However, there may be certain cases of abuse and we have begun to investigate these cases mentioned in the U.N. report,” he said. “We will take actions accordingly.”

But he said that while the Afghan government takes the allegations in the report very seriously, “we also question the motivations behind this report and the way it was conducted.” He did not elaborate.

The NATO military alliance responded to the most recent report by stopping transfers of detainees to seven facilities in Kabul, Laghman, Herat, Khost and Kunduz provinces — most of them the same facilities that were flagged a year ago. The transfers were halted in October, when the U.N. shared its preliminary findings with the military coalition.

“This action is a result of concerns over detainee treatment at certain Afghan detention facilities,” said Jamie Graybeal, a spokesman for the international military alliance in Kabul.

He said there has been no suspension of transfers to the massive detention center next to Bagram Air Field outside of Kabul. That facility has been particularly contentious because the U.S. has held back from transferring all the detainees it holds there to Afghan custody.

But as international troops draw down in Afghanistan, there will be fewer people to monitor the Afghan detention centers. Allen said in his letter that the NATO military alliance planned to focus on monitoring only a subset of Afghan facilities in the future.

And even the manner in which the U.N. report was compiled and released shows the waning influence of Western allies over the Afghan government. Both last year and again on Sunday, the report was released without a news conference. Instead, it was quietly posted on the U.N. website in what appeared to be an effort to avoid publicly antagonizing the Afghan government that it criticizes in the report.

“I think it’s being dealt with in the appropriate way. Maybe we don’t need to do it publicly,” Gagnon said, noting that there have been plenty of discussions with the Afghan government about how to improve the prison system.

Asked what progress had been made toward improving the prison system since 2011, Gagnon was at a loss to give an example. But, she stressed: “There has been quite a lot of effort.”