Story highlights CNN's Ivan Watson speaks to ISIS fighters being held by Kurds in northern Syrian prison

One prisoner claims ISIS paid him $3,600 to plant a bomb that killed his nephew

Another prisoner, 19, says many fighters he met were foreigners, including one Chinese jihadi

CNN has no way to confirm if prisoners were telling the truth or being coached

The blindfolded prisoners are brought into the dank gray room, one by one, and begin to tell us their stories.

We're in a prison run by Kurdish militants here in northern Syria. The Kurds won't allow us to see the cells where the prisoners are being held. Their prisoners, they say, are members of ISIS.

When the first detainee sits down, I ask the guard to please remove his blindfold. He blinks in the bright light and clearly looks surprised to see a foreigner sitting in front of him.

The second prisoner who arrives trembled with fear when he was brought in. I introduce myself to each detainee as an American journalist.

"You don't have to talk if you don't feel comfortable," I add. Each man speaks, though some cast darting glances at the prison guards who watch each interview.

A man named Suleiman says he's from Syria, and claims that he was forced to join ISIS out of fears for his family's safety.

He says he never traveled to ISIS-controlled territory, but confesses to being part of an ISIS cell that planted and detonated a remote control car bomb outside a Kurdish base in this Kurdish enclave. He believes the bomb killed his own nephew -- and says he received about $3,600 for the job.

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"They said they were fighting for Islam and justice," Suleiman tells us. "They were lying to us. They took advantage of our minds and our poverty."

ISIS has seized huge chunks of Syria and Iraq in recent months, beheading Western journalists and nonbelievers as it strives to establish an independent "Islamic State" in the region.

The terror group has been locked in a battle with Kurdish forces in the northern Syrian border town of Kobani since mid-September. The United States and its allies are bombing ISIS positions there, but airstrikes have yet to pry Kobani from the group's hands.

The next prisoner the guards bring out is barely a man. His name is Kareem, and he says he's 19 years old.

Kareem tells me he was paid $2,000 to fight alongside ISIS on the Syrian frontlines for more than a year -- and he has the battle scars to prove it. Lifting up his shirt, he reveals a gruesome pink and brown scar on his stomach.

"I was shot in the stomach three times," he says. He also has ugly scars on his right arm from another bullet wound. He claims ISIS drugged fighters before they went into battle.

"They gave us drugs," Kareem says. "Hallucinogenic pills that would make you go to battle not caring if you live or die."

Kareem says he fought for a year all across ISIS-controlled territory. He says other fighters he was with were promised wives by ISIS. Most of the fighters were foreigners, he says, and he had difficulty communicating with them because they didn't speak the local Syrian dialect of Arabic. Kareem says he even met a fighter from China at one point.

Before his capture by the Kurds, Kareem claims he saw ISIS behead many of its prisoners.

"Whenever ISIS goes into an area ... the people there who don't adhere to their Islamic law are apostates," he says. "Everything has to follow ISIS' way. Even women who don't cover their faces ... women would get their heads chopped off."

The final prisoner was Jaber, a former teacher and father of two who also confessed to a car bombing.

I ask Jaber what he would have done if he'd found me while he was on patrol with ISIS.

"Your fate would be death," he tells me. "And there are different kinds of death -- they would torture you for sure, they might decapitate you, or cut off your hands. They will not simply shoot a bullet in your head."

When we finished speaking, a guard draped Jaber's blindfold back around his head and led him out of the room.

It's impossible for CNN to confirm whether anything the prisoners told us was true -- or whether these men had merely been coached on what to say by their captors.

They also appeared to have little information about what was going on in the outside world.

One of the men, Suleiman, looks shocked when I tell him that a U.S.-led coalition that includes Saudi Arabia and the United Arab Emirates is conducting an aerial campaign bombarding ISIS targets.

"I hope they kill all of them," Suleiman says, with what appear to be tears welling in his eyes.

All three men say it was a mistake to join ISIS. And they are begging their Kurdish captors for forgiveness.

But the Kurdish guards running this prison say that if set free, every one of these men would likely go back and rejoin ISIS.