KARACHI: During some sleepless nights when his stark bedroom walls remind him too much of his old prison cell in Afghanistan, Jan Sher Khan scans Internet dating sites he'd heard about from US soldiers who once guarded him. 

The 24-year-old Pakistani never contacts anyone on the dating sites. He doesn't know how he'd tell them he spent more than six years in the US military prison of Bagram after being detained as a 16-year-old and accused of being a suicide bomber.

More than 2,500 juveniles have been detained in Afghanistan, Iraq and Guantanamo Bay by the United States since 2001, according to a UN report.

Most, like Khan, are now free, but many are struggling to rebuild their shattered lives.

"Sometimes I feel like I'm still in prison," said Khan, who, like all foreign prisoners at Bagram, was never charged with a crime.

"They put me in jail for six years. No proof, nothing. I spent my youth behind bars," he said, adding that he and other young detainees were beaten repeatedly during the first few months of their detention.

A US court found two adult detainees had been beaten to death at Bagram in 2002, using techniques similar to those described by Khan.

The US government said such cases of abuse are rare.

"Although there have been substantiated cases of abuse in the past, for which US service members have been held accountable, our enemies also have employed a deliberate campaign of exaggerations and fabrications," said Lt. Col. Todd Breasseale, a spokesman for the Department of Defense in Washington.

"All credible allegations of abuse are thoroughly investigated, and appropriate disciplinary action is taken when those allegations are substantiated," said Breasseale.

US officials in Afghanistan, Pakistan and Washington, contacted by Reuters, all declined to discuss individual cases of Bagram detainees.

Reuters could not independently verify some aspects of the accounts provided by the detainees interviewed for this story. Journalists are not permitted inside Bagram.

Khan said the abuse he suffered inside Bagram has left him with frequent headaches and mood swings. He said he can no longer concentrate for more than a few minutes.

Khan is seeing a Pakistani army psychologist but his problems and the stigma of being labeled a "terrorist" because of his time in Bagram make it difficult to rebuild his life - to find a job and eventually a wife.

"All my friends are married. Some have kids. We are not really close any more," said Khan, who wants to marry but fears no woman will have him.

Foreign prisoners at Bagram have no trials, only review boards staffed by US military officers.

Prisoners do not have the right to see classified evidence against them and are represented by a US military officer, not a civilian lawyer. The boards evaluate evidence against them and whether they might pose a future threat to US forces.

The process falls "severely short of fair trial standards," said Sarah Belal from Justice Project Pakistan, which has filed a case in Pakistan on behalf of some of the families.

The US government says detention is necessary to stop released prisoners from returning to the battlefield. Some have done so, it says.

"Detention in wartime has long been recognized as legitimate under international law. Just as we do with prisoners of war in more traditional armed conflicts, we acknowledge that the threat they pose may change over time," said Breasseale.

A case filed in the United States three years ago by the International Justice Network is challenging the US right to hold foreign prisoners captured abroad indefinitely in Bagram.

Khan said he was told for more than two years that the military review boards were willing to let him go but were waiting for a response from the Pakistani government.

The Pakistani government said they always responded promptly to requests from the United States.

Belal is working on a case in Pakistan to force the Pakistani government to do more to bring its citizens home from Bagram.

Khan said he ran away from home as a teenager to escape beatings from his strict military father, who disapproved of his poor grades, his friends and his drinking and smoking.

He said he went to Afghanistan to find a job because he had read about US-funded construction projects there in the news.

But within a week, he said, he was arrested after Afghans made up accusations against him to collect cash for a tip-off.

He said he spent the next six months being beaten by interrogators every few days. Sometimes he was shackled to a chair, other times hung from the ceiling by his ankles.

"Everyone got the treatment. It was just -- is it going to be for one month or for six months?" Khan recalled. "They asked me stupid questions, like 'where is Osama bin Laden?'. I said, 'I'm 16. You think he is going to meet me?'"

Khan was eventually moved from his single cell to the general prison population and the beatings stopped. He was freed last year. A Red Cross spokesman confirmed the organization flew him back to his hometown of Peshawar in Pakistan.

Local Pakistani security services are now frequent callers at his parents' house. Neighbors shun him; no one wants trouble with the intelligence services.

Pakistani Kamil Shah said he was detained in 2004 at the age of 16, shortly after crossing the Afghanistan/Pakistan border with a sick friend needing medical help. He was held for five years in Bagram, without charge, until his release in 2009.

"They said I was a Talib. They said you will be here forever," he said down a crackly phone line from northern Pakistan. Khan confirmed Shah was in Bagram when he was there.

Shah also said he was eventually freed after he learnt enough English to speak directly to his US interrogators and convince them he was telling the truth.

US soldiers also told him several times they were willing to release him but were awaiting a response from Pakistan, he said.

"I was innocent. I lost my education. I lost everything," said Shah, who had three years until his high school graduation when he was detained.

Shah said he was beaten in the first months of detention.

"Clearly in the early days there was ongoing torture at Bagram," said Andrea Prasow, a senior counter terrorism counsel from the New York-based Human Rights Watch. But the situation had improved, she said.

"Since detainees were moved to a new prison by the Obama administration (in late 2009), we haven't heard credible accusations of mistreatment at that level."

Conditions at Bagram are monitored by the International Committee of the Red Cross. But their reports are not public.

"The ICRC ... shares its concern according to international law with the detaining authorities," said Robin Waudo, the organization's Kabul-based spokesman.

US officials say no decision has yet been reached on what will happen to the 50-plus foreign prisoners in Bagram, half of them Pakistani, when the US hands full control of the prison to the Afghan government in September.

Pakistani government court documents lodged in Lahore High Court and dated December 2011 say there are still three juveniles inside Bagram, one aged 15 and two 16.

An adult and the 15-year-old, Mohammad Tayyab, though cleared for release by both the United States and Pakistan, are still being held because they have no exit visas, a Pakistani government official said.

US authorities say they are aware of only one juvenile prisoner, aged 17, and no child prisoners.

Some prisoners, like Hamidullah Khan, were arrested as children and have grown up behind bars.

A photo of a young, dimpled Hamidullah grins down from a wall of a stuffy concrete room in Karachi, Pakistan's largest city. It's the last photo taken before he disappeared on the border between Afghanistan and Pakistan. He was 14 years old.

Hamidullah vanished in 2008 after his father sent him to collect the family's belongings from their village near the border. On his way home he telephoned from a bus stop, but the next thing his family knew, he was in Bagram.

A Pakistani government memo says he was captured in Khost province in Afghanistan for "attacks on coalition forces" but gives no details.

"Why don't they tell us what he has done?" asked his father Wakeel Khan, a former soldier now barely making a living as a security guard. "If he is guilty, I will kill him myself," he said gruffly, as his other sons silently looked on.

More than 300 children were recruited as fighters in Afghanistan in 2011, according to a UN report on children and armed conflict. The youngest was an 8-year-old girl. But Hamidullah's family say he had no interest in the insurgency.

The Red Cross recently set up monthly video calls between Hamidullah and his family. If he mentions conditions in Bagram or his arrest, the lines are cut.

While Hamidullah has been detained, his mother Din Rozen has been fasting from sunrise to sunset, believing her suffering strengthens her prayers for her son to come home before she loses her sight due to cataracts.

"He's my child...Who is taking care of him now?" cried Din Rozen, using her headscarf to dab away tears.