WILLIAM BRANGHAM: It's been five years# since the Islamic State, or ISIS,## was defeated the U.S.-led# military campaign in Syria.

But today, nearly 10,000 ISIS fighters remain# jailed inside Syrian detention centers.

Human## rights groups call conditions in the prisons# abusive, and local authorities warn they are## a breeding ground for radicalization# and could help spark an ISIS revival.

Special correspondent Leila Molana-Allen traveled# to Northeast Syria to meet high-security prisoners## and the regional forces that# are still battling ISIS.

LEILA MOLANA-ALLEN: The horrors of ISIS, a# threat long past, the world believed.

So,## ISIS-K's devastating attack on# Moscow came out of the blue.

But for the Middle Eastern governments# and civilians who have been warning of## the group's resurgence for many months now, it# was all but inevitable.

Here in Northeast Syria,## where thousands of ISIS fighters are# locked up, unsentenced in crumbling jails,## and tens of thousands more ISIS-linked families# languish in displacement camps, the Syrian## Democratic Forces have been begging their# Western allies to address the growing threat.

SIAMAND ALI, Military Spokesperson, Syrian#Democra... risk for them.

This kind of thinking has# given the chance for ISIS to reorganize## themselves.

They rebuilt new groups and# they began a new strategy to start again.

LEILA MOLANA-ALLEN: The vast desert between# Hasakah and Deir ez-Zor, the Badiya,## is one of Syria's most deadly areas.

ISIS# controlled this territory for several years.

The rugged, open terrain here makes it easy# for militants to conceal weapons and fighters,## harass local farmers for# money and plan operations.

We're on a patrol with the SDF through the lawless# desert area leading up to the Iraqi border.## There are many villages here where people still# support ISIS and some of them hide sleep cells.

Whenever there's an alert, the commandos get# out to investigate and speak to villagers.## Some support ISIS.

Many others are terrorized by# them.

They're trying to catch security threats and## eliminate them before they can carry out an attack# and to remind everyone who's in charge here.

Commander Zinar knows the danger.

He was# permanently maimed in a 2016 ISIS explosion.

COMMANDER ZINAR, Special Forces, Syrian Democratic# Forces (through translator): Our goal is to track## down ISIS sleeper cells who are attacking an.. a lot of military operations in this area,# but, still, they're reorganizing themselves.

LEILA MOLANA-ALLEN: With so much ground# to cover and such a high threat level,## more and more militants are# slipping through the net.

The## huge ISIS prison break two years ago# was staged from these sprawling sands.

Dozens of sleeper cells attacked using suicide# bombs and armed trucks; 1,000 prisoners escaped.## Over 100 were never recaptured, and 120 SDF# officers and local civilians were killed.

The attack ended after 10 days only thanks# to coalition airstrikes.

Local authorities## warned they couldn't defeat another escape# attempt alone if U.S. forces leave Syria.

Nureddine Berham is a high security# prisoner at Al Sina'a.

We were given rare## access to speak with him before the Moscow# attack.

A militant jihadist to his core,## he's been joining up with Islamist# militias to fight Western ideology## since he traveled to Pakistan to# support Osama bin Laden in the '90s.

Originally Jordanian, the rest of# his family are American citizens,## and he claims he traveled to the U.S.# regularly on visas until the mid-2000s.## In Syria, he signed up with ISIS as# a suicide bomber, but was captured.

NUREDDINE BERHAM, Imprisoned ISIS Fighter# (through translator): I was waiting for my## turn, and eagerly.

So it didn't# happen.

Mo.. if you were outside of this prison, I'm# not going to tell that I'm -- if I'm able## to make every -- every minute, a martyrdom# operation, I will do it every second.

LEILA MOLANA-ALLEN: Berham was at# the forefront of the prison break,## handing weapons to other inmates.

He# says the prisoners managed to smuggle## in weapons and mobile phones to receive# instructions from the attackers outside.

NUREDDINE BERHAM: The plan was, when we# hear the bomb, when we hear the explosion,## we have to break the walls and just# break out.

In like 15 or 20 minutes,## we were taking control of the whole prison.

LEILA MOLANA-ALLEN: Authorities here# wouldn't let us see inside the cells.## Berham says the prisoners live in horrendous# conditions, often more than 20 to a cell,## and with many suffering from# fungal infections and tuberculosis.

But that lack of oversight also allows# them to continue their radicalization,## operating a mini-Dawlat, Islamic State, unimpeded.

NUREDDINE BERHAM: And inside the prison, we# were still Dawlat.

We were still implementing## Sharia.

We would rather die than to# live this kind of life.

We're fighters.

LEILA MOLANA-ALLEN: Berham says they will# keep trying to break out until they succeed.

You have just told me you want to blow yourself# up at any opportunity.

You want any opportunity## to fight America, to fight this government.# How and why could you possibly be released?

NUREDDINE BERHAM: It doesn't matter how long we# stay in prison.

We're not going to change it.

This## is the 11th time I be in prison.

And every time,# I go back, and, every time, I go back to fighting.

LEILA MOLANA-ALLEN: The prison was# destroyed and the prisoners are now## housed in a new facility.

But the# attack showed that keeping so many## dangerous militants in these conditions with# limited security forces is unsustainable.

There are thousands of ISIS-linked prisoners# being held here in a city of fewer than## 450,000 people.

Many of those jails are in# residential areas.

The one just behind me,## which holds some of the most# dangerous captured ISIS fighters,## is just meters from a busy shopping street# and children playing in front of their homes.

Mohammad lives on this street.

He# knows just how real that threat is.

His## young family was at home when the shooting# began, then banging on the front door.

MOHAMMAD, Hasakah, Syria, Resident (through# translator): One of them was pointing a gun.## The others walked in.

They were all dressed# in prison uniforms.

Then the clashes,## shelling and shooting started.

They killed# my cousin.

They shot him in his head here,## and it came out from the other side.

LEILA MOLANA-ALLEN: Escaped fighters# occupied homes, taking residents hostage,## as grenades rained down over the narrow streets,# beheading several residents who didn't obey them.

Mohammad's 5-year-old son, Adam,# hasn't slept through the night since.

MOHAMMAD (through translator): My son calls, "Dad,## it's ISIS" in his sleep.

"Daddy, will# ISIS escape?

Wil.. What have these children done to live this horror?## God forbid if they flee the prison# again.

What will happen to people?

LEILA MOLANA-ALLEN: The Syrian Democratic# Forces estimate there are at least 10,000## ISIS fighters still active in the# area, and that number is growing.

Now, in a speech posted online, ISIS leaders# have called on their supporters to plan fresh## attacks on cities around the globe.

Former# U.S. Army Colonel Myles Caggins was the## coalition spokesman in Iraq and Syria at the# height of the battle to defeat ISIS.

For him,## Northeast Syria's overflowing# jails are a ticking time bomb.

COL. MYLES CAGGINS (RET.

), U.S. Army:# The world doesn't really want to deal## with these 10,000 detainees.

President# Biden and his administration have.. the policy of the previous administration, where# nobody really wants to talk much about Syria.

The American public, in particular,# does not hear much about ISIS until## there's something like a massive attack# that happened in Russia.

It is important,## though, for the world to pay attention to ISIS.

There are wealthy individuals who support# ISIS' ideology.

The scale and type of attacks## that they conduct do not require a lot# of money, but they're able to get a large## effect out of them by having these attacks# in highly visible places and recording the## attacks and sharing it as propaganda,# propaganda that is desired -- designed## to inspire other members of ISIS.

It's# designed to inspire potential recruits.

LEILA MOLANA-ALLEN: Officials here# are threatening to carry out their## own trials if an international# tribunal isn't established,## but, in, reality courts here don't have the# jurisdiction to try many of these prisoners.

With foreign nations refusing# to take back their citizens,## fighters sit in wait, plotting their# escape and the group's return to power.

NUREDDINE BERHAM: We have to fight# to the last drop of our blood.

We## are more insisting now to fight you,# America, and all that is fighting with## you (SPEAKING IN FOREIGN LANGUAGE)# until it's either us or you guys.

LEILA MOLANA-ALLEN: For the# "PBS NewsHour," I'm Leila## Molana-Allen in Al Sina'a prison, Northeast Syria.