The stern police officer doffed his peaked uniform cap and placed it carefully on his parlor carpet. He drew his asthma inhaler from his pocket and set aside his teacup. Then he knelt and twisted his gaunt frame into a series of contorted positions, grimacing in pain and panting for breath.

Col. Syed Nabi Siddiqui, 47, was acting out the humiliating treatment he said he received during 40 days as a detainee in three U.S. military prisons last year. He said his captors made barnyard jokes about his manhood, bent him into painful postures, photographed him naked, prevented him from sleeping, beat and stoned him, and taunted him while he relieved himself in a bucket.

"I kept begging them for water and they would spray something on my face, so I had to lick the drops," Siddiqui recounted at home in his village in Paktia province, as four of his young sons listened silently. "They asked me stupid questions like did I know Fidel Castro. . . . They covered my face and told me they put a snake and a scorpion on my neck. I thought I was going to die, but they were always laughing, like it was all a joke."

Siddiqui's story is the one of the first and most detailed allegations of abuse by U.S. military forces and other American security agents who operate detention centers throughout Afghanistan. Hundreds of prisoners have passed through these centers in the past two years, and at least three are reported to have died. U.S. officials have repeatedly refused to discuss detention conditions and have allowed Red Cross delegates to visit only one of the facilities.

Human Rights Watch, a New York-based group, charged this week that mistreatment of prisoners in U.S. custody in Afghanistan was a "systemic problem." The group reported that detainees had been beaten, stripped, exposed to extreme temperatures and photographed while naked. It said some of the abuses were similar to those recently exposed and photographed in Abu Ghraib, a large prison run by the U.S. military in Iraq.

U.S. military officials in Kabul expressed shock and concern last week over Siddiqui's account, and promised to begin investigating immediately. On Saturday, a U.S. military spokesman in Kabul said officials had received a second complaint of prisoner abuse and would also investigate it, but he provided no details. According to press reports, the former detainee said he was hung from a ceiling and force-fed water while held last year in one of the same prisons as Siddiqui.

"The coalition forces are committed to ensuring that all detainees are treated humanely and consistent with international law," Lt. Col. Tucker Mansager said at a news conference in the Afghan capital. "Our investigation is proof that we are concerned about these things."

In the past two years, some Afghans released from U.S. custody in the main detention facility at Bagram air base, north of Kabul, have described being hooded, held in groups in cramped wire cages, made to assume painful positions for hours at a time, deprived of sleep and subjected to other forms of duress.

But Siddiqui's account of abuse that allegedly occurred at U.S. bases in Paktia and Kandahar provinces is the first to emerge from the smaller, rural detention facilities run by various U.S. military and intelligence forces. It is also the first to allege sexual humiliation of the type described and photographed in Iraq. Although his story became public only this week, he complained of mistreatment to an Afghan human rights group after he was released last August.

Siddiqui, a veteran police officer in Paktia, said his ordeal began last July, shortly after he complained to the newly appointed provincial police chief about corruption and abuse by another police official. He said he was called to the chief's office and found several U.S. military officers there who asked for his assistance with some investigations and escorted him to their base outside the city.

There, he said, he was thrown into a locked room and held prisoner for 22 days. He said he was questioned by teams of young Americans who wore "shorts and T-shirts" and were assisted by masked Afghan translators. He said he acknowledged working briefly as a police officer under the Taliban, the repressive Islamic militia that ruled Afghanistan until late 2001. But he said many questions seemed irrelevant or ridiculous, such as whether he had heard of Castro, the Cuban president, or various Afghan militia leaders.

Siddiqui said his captors indulged in frequent sexual taunting and harassment that included poking fingers and objects in his rectum, photographing him while naked, making farm animal sounds and asking which kind of beast he preferred for sex. The worst moment, said the father of nine, was when he was told his wife and daughters had become prostitutes in his absence.

"They were laughing when they said this," Siddiqui recounted with a deep sigh, his eyes reddening. "I told them please, I am a police officer and Muslim. I have asthma and it is hard for me to breathe. I am not al Qaeda or Taliban. I fought against the Russians, and I was happy when the Americans came to Afghanistan. I asked them to please let me go home to my family, but they paid no attention."

After three weeks, Siddiqui said he was hooded, shackled and taken by helicopter with a large group of detainees to another base, which he later learned was near the southern city of Kandahar. There, he said, his captors were all wearing military uniforms. During about one week at that base, he said, he was beaten and forced into various painful positions, but questioned only cursorily and not about any serious matters.

As in Paktia, he said, the hardest thing to bear was physical humiliation. He said groups of detainees were kept together in large wire cages, where they were forbidden to speak to one another but had to share a common bucket as a toilet. They were constantly watched and denied the privacy that is extremely important in Muslim societies. All wore zippered jumpsuits, which they had to lower completely when they used the bucket.

"We begged them to let us use a real toilet, because it was so shameful, but they just laughed at us," Siddiqui said. He also said U.S. soldiers threw stones at the caged detainees and forced them to roll naked in mud. He was constantly thirsty and short of breath, he said, and once lost consciousness and woke up in a military clinic, but was returned to the cage.

After 12 days, the policeman was flown with a group of prisoners to Bagram, where he said the treatment changed. He was given a copy of the Koran and a prayer rug, and he said several U.S. military officers apologized for his suffering. After one week, he was given a release document saying he posed "no threat" to U.S. forces or interests in Afghanistan. It said he had been in U.S. military custody for only seven days.

Siddiqui's story cannot be corroborated, but U.S. military officials in Kabul have said that if it is true, it would include "potentially criminal behavior" on the part of U.S. personnel. They also said they had no knowledge of his case until it was reported by the New York Times this week, but officials of the Afghan Independent Human Rights Commission said they had brought Siddiqui's complaint and others to the attention of U.S. military officials last year.

Siddiqui's boss, Gen. Gul Hai Sulaimankhel of the Paktia police, confirmed the colonel's account of his arrest. Sulaimankhel said he shared Siddiqui's suspicions that he had been denounced as a Taliban supporter by the police officer he criticized, a controversial figure who vanished from the province months ago.

In an interview in Gardez, Paktia's provincial capital, Sulaimankhel said that he was "astonished" by Siddiqui's account and that the colonel had not told him about any abusive treatment when he returned to work last August, more than a month after being taken to the U.S. military base.

"I am still spinning from this news," the general said. "I have seen other prisoners come back from Bagram, but I never heard such a complaint."

Sulaimankhel has worked closely with U.S. military officials, whose base near the city is also a center for regional assistance and security programs. "They have helped me a lot, but I know nothing about their jails," he said. "We hate to have the Americans get a bad image, but incidents like this make everyone disappointed."

Siddiqui, who said he still wakes up shaking from nightmares, insisted that he bears no ill will toward U.S. forces in Afghanistan and believes his abusers were "a few bad people." After his release, he participated in a U.S.-run training program for law enforcement officers. During a lengthy interview Friday, he proudly displayed his graduation certificate.

Siddiqui lodged a complaint at the Gardez office of the Afghan human rights commission last year, and officials of the organization said they considered him credible.

The solemn, bearded officer said he had not previously revealed the full details of the abuse because they were too shameful and he feared reprisals. Then several weeks ago, he said, he was amazed to see the photos from the Iraqi prison on television.

"My children were watching and they asked me, 'Father, did the Americans do those things to you, too?' " Siddiqui said. "I told them, 'No, my sons,' but they did. They did everything but put me on a leash."

Col. Syed Nabi Siddiqui said the U.S. forces who allegedly abused him "were always laughing, like it was all a joke."