Bunk beds in dormitories for Islamic State fighters at a training center in the Zuhoor neighborhood of Mosul. (Loveday Morris/The Washington Post)

The bunk beds that fill the rooms sleep more than 80 Islamic State recruits. On the walls, posters detail the components of Russian Kalashnikovs and American assault rifles.

One sign reminds the trainees that victory comes from long fights and pain — rewards come later: “Remember that we didn’t come for this life, we came for the afterlife.”

Spread across several large houses, the “Sheikh Abu Samaya Ansari Camp” was discovered this week by Iraqi forces as they pushed deeper into the northern city of Mosul, which Islamic State militants have been fighting bitterly to retain.

It is the first military training center that the Iraqi forces have found in the city since they began an offensive to retake it just more than six weeks ago.

Since then, the Islamic State’s grip on its most prized urban center in Iraq has slipped. But the group is still inflicting heavy casualties on advancing Iraqi forces, waylaying them with car bombs and street-to-street fighting.

An Iraqi counterterrorism officer looks at a list of city rules on the wall of an Islamic State training center. (Loveday Morris/The Washington Post)

The documents and learning aids left at the training center highlight the mix of guerrilla and conventional warfare tactics — combined with religious indoctrination — that make the group such a formidable foe. They show a detailed level of military planning and training, drawing manpower and expertise from around the world.

[‘I thought, this is it’: One man’s escape from an Islamic State mass execution]

The sign for the training camp’s armory was written in both Russian and Arabic. A carbon-dioxide canister, probably for use in an air rifle for target training, was also marked in Russian.

Thousands of Russian passport-holders have traveled to Iraq and Syria to join Islamic State militants, making up as much as 8 percent of the group’s foreign fighters, according to Europol, the European Union’s law enforcement agency. Most come from the predominantly Muslim North Caucasus region.

“This was an initial step for new recruits,” said Brig. Gen. Haider al-Obaidi, a commander with the Iraqi counterterrorism troops that retook the camp and interviewed residents in the area. “We think they were mostly Iraqi, with some foreigners. They were mostly training on Russian weapons, so maybe some foreigners were training them.”

Neighbors said the fighters did not interact with them.

“We’d see them go in and out, but they’d have their faces covered,” said Mohammed Muthafer, who lives across the street.

“This is my room; I watched them sometimes,” he said, pointing at his house. “But they covered all the windows.”

Buses would ferry recruits in and out, but their windows would also be blacked out so it was not possible to see them, he said. A building next door was previously used to house women, including a Russian and one from Tajikistan, he said, adding that suicide bombers would “party” with them before their final missions.

Since seizing Mosul 2 1 /2 years ago, the Islamic State has embarked on an ambitious program of state-building, complete with bureaucracy and thorough record-keeping. The documents that the militants left behind when they moved out more than a month ago shed light on the group’s inner workings.

[Iraq has never seen this kind of fighting in its battles with ISIS]

One printed sheet detailed the equipment that fighters were told to take on operations. In addition to weapons and ammunition, each group should have two TNT mines and 10 molotov cocktails, it said, as well as a shovel, ladder, hammers and nails, and stretchers.

Fighters also were instructed to take two large smoke bombs, or four small ones, night-vision goggles and binoculars. The list continued in minute detail: a knife, torch, lighter, first-aid kit and small notebook and pen.

A set of dumbbells lay in a hallway of the center, and half-used packs of steroids in one room. In another, bundles of long, beige Afghan-style tunics and pants favored by the group were strewn across the floor.

One sign urged the “mujahid” to keep clean and quiet.

The recruits were apparently tested on their knowledge of weapons.

“Name the firing positions for a 7.62mm Kalashnikov,” read the first question on one exam that was left behind. “What’s the maximum range?”

Other documents detailed the health of fighters, noting their pulse rates and blood pressure.

It is unclear how old the recruits were, although Muthafer said the militants targeted young teens in the area. Since beginning to take ground in Iraq nearly three years ago, Islamic State militants have tried to build their legacy by focusing on indoctrinating the next generation.

“In the mosques they’d order us to go for jihad, but you’d have to really want it and get a recommendation,” he said. “People my age, they didn’t really bother, but 12- or 13-year-olds, they’d talk to them in the mosque and in the street and try to convince them.”

The Islamic State has separate training camps for its “cubs of the caliphate,” but there were indications that some of the trainees housed at the center might have been young. Outside one building, an exercise book included lessons on the basic tenets of Islam. On one page, a short entry titled “The aeroplane,” was written in a childish scrawl.

“At morning the sound of the airplanes is very loud, it’s choking us,” it read. “The infidels have no mercy. We are very afraid of the pilot.”

On the wall of a large room, a list of rules for the city was laid out like a constitution.

“All people, you have tried the secular regime, you’ve lived under many eras,” it said. “Now this is the era of Islamic State.”

It praised the group’s “victory in the city” and the release of thousands of prisoners held in Iraqi jails. “Islamic State keeps moving,” it said. “We will never go back.”

But slowly, Iraqi security forces are winning back land here in the Islamic State’s self-proclaimed caliphate. The car bombs, which at one point numbered around 25 a day on this eastern front, have dropped to around five, counterterrorism officers said.

The militants’ resources appear to be dwindling, and much of the population of Mosul has turned against them.

“I’d wish you’d push them out,” said one man as he approached the counterterrorism forces outside the former training camp, pointing toward the streets behind him as gunfire rang out.

Read more:

Islamic State is kidnapping thousands of people to use as human shields

Islamic State has unleashed over 600 car bombs in Mosul battle

Today’s coverage from Post correspondents around the world

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