KABUL, Afghanistan -- Last summer, as the Islamic holy month of Ramadan was drawing to a close and the Islamic celebration of Eid was about to begin, a Taliban fighter was seen distributing propaganda leaflets in the Afghanistan capital of Kabul on orders from his group's mullahs. He was also attempting to transfer an improvised explosive device (IED) that he made himself to another fighter -- the device carefully hidden at the bottom of a basket of eggs.

It was then that he was nabbed by covert soldiers working for Afghanistan's National Security Directorate (NDS), which functions like the FBI, who had been tracking him for some time.

Around two weeks earlier, the Taliban member had opened fire and wounded three police at a checkpoint in Kabul, but had managed to escape. Not long before that, 20 days before the start of Ramadan, he also shot dead a senior judiciary official in the city.

The fighter's name is Hanifgul. He is 21 years old.

"That judge was making a case against the Taliban," he tells Fox News defensively from the NDS detention facility in Kabul that he now must call home. Hanifgul added that his brother, who has since escaped to Pakistan, was his cohort in the attacks.

Hanifgul, an accused Taliban fighter (Hollie McKay/Fox News)

Hanifgul wears a brown, orange-trimmed Afghan prison dress and pants, a traditional black "pach" prayer cap and has a small beard. His skin is mottled with post-adolescent acne and he exudes defiance and pride.

After finishing ninth grade, Hanifgul started working with his father, who is primarily a driver, assisting him to clean homes and offices. He says he was recruited into the Taliban by a friend from Logar province early last year, and he then traveled to a madrassa he called "Escape" in Peshawar, Pakistan, for the first steps of religious "education."

Over the course of almost three weeks, the Taliban worked to instill in the students an anger at infidels as regularly as they fed the students their diet of nan bread and rice. The Taliban also said they aimed to use 21st century warfare and weapons to turn Afghanistan into their idea of seventh-century Arabia.

Hanifgul was soon selected to continue his training by becoming an expert at making an improvised explosive device (IED). Once a week for more than a month, he recalls, he attended classes in a private home in Shamshato, a sprawling refugee camp just east of Peshawar, and was taught three main subjects: how to collect intelligence, how to use explosives and how to make explosives.

"Thirty minutes is all I need if the material is there," Hanifgul says, referring to his IED-making and bomb-making skills.

Hanifgul stresses that not only were they mandated to fight the Afghan government and foreigner invaders, they were also ordered to fight ISIS.

"Everything I did I regret, but not killing ISIS [fighters]," he boasts "They are not Islam."

Oct. 20, 2009: Taliban militants are shown after they attacked a military convoy near Kabul, Afghanistan. (AP)

He professes to have shot dead at least 45 to 50 of their members in Bati Kot, a district of Nangarhar last year, before proudly "liberating" the villagers under ISIS command.

Hanifgul also notes that he initially traveled to Pakistan in a car via the Torkham Gate, the main international border crossing for trade between Afghanistan's Nangarhar province and Pakistan's federally administrated tribal areas. There, Hanifgul says, he was greeted and then accompanied by a Taliban member. Pakistan’s border guards asked no questions. Hanifgul returned the same way.

Another young Taliban fighter, Haibatullah, interviewed separately by Fox News also trained in Pakistan and claims there were no issues entering or exiting Afghanistan. He says he and a friend departed from Afghanistan’s Ghazni province and were met by a senior Taliban member at the Torkham Gate.

"We were stopped at the checkpoint and the member just flashed a pass to the Pakistan guards and said, 'They are with me,’" he recalls, indicating that they were waved through with no further questions asked.

After two months of training in Quetta, Haibatullah says he returned with friends to Afghanistan via an "irregular" non-paved road with complete ease.

According to one high-ranking NDS official, who requested anonymity, the Afghanistan conflict is certainly "not limited to our borders."

"I don't know a single case that did not have some ties to Pakistan," the official points out.

Both Taliban recruits say that they were not paid a salary by the group. Food was provided for them and expenses covered. Now, behind bars, they each claim to regret their Taliban involvement.

"Assisting your parents is the only jihad," said Hanifgul, who cautions anyone thinking of joining the terrorist outfit.

Anyatullah, an accused ISIS fighter (Hollie McKay/Fox News)

Meanwhile, another detainee, Anyatullah, allegedly worked as a facilitator for the far smaller -- but still sophisticated and lethal -- ISIS.

"I didn't choose to be ISIS," said the 22 year old, who wore brown prison attire and sported a small beard. "I didn't even know I was ISIS until I was being investigated."

Anyatullah vows that he was simply working in Kabul as a taxi driver when his sister's husband four months ago asked him to take a man and burka-clad woman from the western province of Herat by the Iranian border to Kabul and then to Jalalabad, the provincial capital of the ISIS stronghold of Nangarhar, next to the Pakistan border.

Anyatullah says he asked no questions and his passengers had no weapons. He then made another trip at the request of his brother-in-law, this time taking two young men from Kabul to Nangarhar. He insists that he didn't take any money, other than having his food and fuel costs covered.

"I was a very clean volunteer," Anyatullah maintains.

However, NDS officials remain suspicious that his role was far bigger than he is willing to admit, with evidence pointing to him shuffling new ISIS recruits from the Iranian border to Kabul and then to the ISIS-dominated regions in Afghanistan's south.

January 30, 2012: Taliban militants hand over their weapons after joining the Afghan government's reconciliation and reintegration program, in Heart. (Reuters)

Two months ago NDS special forces arrested him in Kabul by following intelligence leads. Anyatullah says his brother-in-law, who he only realized was an ISIS member after he himself was arrested, was previously in Bagram prison for being involved in terroristic activity. But for an unclear reason, around a year ago, he was released.

Anyatullah believes his brother-in-law is currently fighting with ISIS in Nangarhar's Bati Kot district.

All the alleged fighters interviewed by Fox News are yet to be sentenced. The process can take anywhere between three months and a year. They are kept in rooms with several others, although one NDS official said that some "extreme cases" are placed in cells alone. The majority of detainees -- the official number cannot be disclosed and changes frequently -- are male Afghan citizens aged between 18 and 35. However, there are some foreign detainees from places like Uzbekistan and Central Asia.

Women and juveniles -- some as young as 8 years old -- have been captured and are held separately. None showed visible signs of torture and they are fed three meals per day. All undergo Islamic studies and a "deradicalization" program of sorts, and are allowed visitors once per week.

Their crimes range from attempted suicide bombing to being gunmen to being informants. If found guilty of terrorist crimes, detainees can expect to spend at least 20 years behind bars. Or face the death penalty.

Various terror organizations are represented among the detainee population, but most belong to the Taliban.

"The Haqqani network are the most psychologically ready for interrogation," one official notes. "They are taught to hurt themselves in prison and then complain to human rights groups and are skilled at obstructing the course of justice. Everything is calculated."