In a room full of would-be suicide bombers at a high security detention centre in the Afghan capital, an elderly cleric quietly reads out verses from the Quran, telling the young men the act of killing oneself is itself a crime in Islam.

"You won't go to paradise. Killing yourself and killing others is forbidden in Islam," he tells the men sitting on chairs arranged in rows in the brightly lit room, and points to pages in the holy book.

Some of them nod, others stare vacantly.

Afghanistan's National Directorate Security, long reviled for abuse and torture of detainees, says it is trying to draw the poison out of the young minds by teaching them the Quran, taking the men to mosques in Kabul to show people praying peacefully and proving their instigators were wrong.

Suicide attacks, unknown in Afghanistan until 2004, have become particularly worrying as newly minted government forces take control of security ahead of the withdrawal of most foreign combat troops in 2014. They account for the highest number of deaths of civilians and military forces after roadside bombings.

The attacks have prompted authorities to fortify government buildings and foreign offices with rows upon rows of blast walls to stop the bombers.

They are also to fight the brainwashing.

"We work with them psychologically, we show them movies and films of atrocities of the Taliban and we also take them to mosques to see thousands of worshippers," said Lutfullah Mashal, chief spokesman of the NDS, which last week gave Reuters rare access to the prisoners under supervision.

"During our interviews with them, we found that most of them do not know what they are doing. They are told false stories about Afghanistan."

Most of the men in the room, some with just the beginnings of a moustache, were Afghans but they had spent their lives in Pakistan. Several million Afghans have moved to Pakistan over decades of Afghan turmoil.

Some of the bombers said they been sent across to Afghanistan after being told Islam was in danger because of the foreign military presence and that women were being raped.

"As a Muslim I wanted to do my part and I agreed to do the mission," said Abdul Wahab. He said he made four unsuccessful attempts to detonate his explosive-laden car on foreign military convoys in northern Afghanistan before he was caught last month.

PROMISE OF PARADISE

Wahab, 18, originally from Kunduz in the Afghan north, but who grew up in Pakistan's garrison city of Rawalpindi where he worked as a porter in a fruit market, said he was approached by a man identified as Sarfraz several months ago.

"I was told stories about Afghanistan, about atrocities by foreigners and the absence of Islamic practices," Wahab said as two NDS agents sat nearby. He was given 15 days of training at a camp for Afghan refugees near the northwestern Pakistani city of Peshawar on how to set off a car bomb.

"I was sent to Mazar-e-Sharif to target the foreigners and despite attempting four times, my car did not explode," he said, speaking slowly in Pashto.

Afghanistan says thousands of Islamic fighters routinely cross over from Pakistan's lawless, ethnic Pashtun tribal lands to carry out acts of violence. It has repeatedly urged its neighbor to act against the militants.

Pakistan says it is doing all it can to fight militancy in its rugged northwestern border region and that Afghanistan is shifting the blame for its inability to tackle chronic instability at home.

Last week, at least 20 Afghan civilians were killed when a pair of suicide bombers detonated explosives within minutes of each other in a crowded part of the southern city of Kandahar, in one of the bloodiest days in weeks.

On Saturday, four French soldiers were killed when a burqa-clad bomber detonated his explosives in a bazaar in the east.

Some of the boys recruited to carry out bombings were told no harm would come to them.

Zahedullah, 17, from eastern Kunar province said he fell in with Taliban fighters at a mosque and they pumped him up to become a suicide bomber to attack foreigners.

"The Taliban told me I won't be harmed, only the Americans would be killed and I would go to paradise," he said.

"I don't want to go to paradise, I want to go home," he said.

Not everyone has had a change of heart. Ahmad Zubair, 18, was caught two weeks ago with a suicide-bomb vest in the eastern city of Jalalabad, near the Pakistani border, where he planned to attack U.S. soldiers.

"I wanted to blow them up. They have desecrated our holy book and made cartoons of our Prophet. As long as Americans are in Afghanistan, there will be suicide bombers," he said quietly, before the NDS agents led him away.