BREMEN, Germany — Believing he was answering a holy call, Harry Sarfo left his home in the working-class city of Bremen last year and drove for four straight days to reach the territory controlled by the ISIS in Syria.

He barely had time to settle in before members of the ISIS secret service, wearing masks over their faces, came to inform him and his German friend that they no longer wanted Europeans to come to Syria. Where they were really needed was back home, to help carry out the group’s plan of waging terrorism across the globe.

“He was speaking openly about the situation, saying that they have loads of people living in European countries and waiting for commands to attack the European people,” Mr. Sarfo recounted on Monday, in an interview with The New York Times conducted in English inside the maximum-security prison near Bremen. “And that was before the Brussels attacks, before the Paris attacks.”

The masked man explained that, although the group was well set up in some European countries, it needed more attackers in Germany and Britain, in particular. “They said, ‘Would you mind to go back to Germany, because that’s what we need at the moment,’” Mr. Sarfo recalled. “And they always said they wanted to have something that is occurring in the same time: They want to have loads of attacks at the same time in England and Germany and France.”

The operatives belonged to an intelligence unit of the ISIS known in Arabic as the Emni, which has become a combination of an internal police force and an external operations branch, dedicated to exporting terror abroad, according to thousands of pages of French, Belgian, German and Austrian intelligence and interrogation documents obtained by The Times.

The ISIS attacks in Paris on Nov. 13 brought global attention to the group’s external terrorism network, which began sending fighters abroad two years ago. Now, Mr. Sarfo’s account, along with those of other captured recruits, has further pulled back the curtain on the group’s machinery for projecting violence beyond its borders.

What they describe is a multilevel secret service under the overall command of the ISIS’ most senior Syrian operative, spokesman and propaganda chief, Abu Muhammad al-Adnani. Below him is a tier of lieutenants empowered to plan attacks in different regions of the world, including a “secret service for European affairs,” a “secret service for Asian affairs” and a “secret service for Arab affairs,” according to Mr. Sarfo.

An External Operations Branch Within ISIS

At least 10 deadly attacks against Westerners have been directed or coordinated by a special unit of ISIS dedicated to exporting terror abroad. In addition, more than 30 people working for this group were arrested before they could carry out attacks.

Reinforcing the idea that the Emni is a core part of ISIS’ operations, the interviews and documents indicate that the unit has carte blanche to recruit and reroute operatives from all parts of the organization — from new arrivals to seasoned battlefield fighters, and from the group’s special forces and its elite commando units. Taken together, the interrogation records show that operatives are selected by nationality and grouped by language into small, discrete units whose members sometimes only meet one another on the eve of their departure abroad.

And through the coordinating role played by Mr. Adnani, terror planning has gone hand-in-hand with the group’s extensive propaganda operations — including, Mr. Sarfo claimed, monthly meetings in which Mr. Adnani chose which grisly videos to promote based on battlefield events.

Based on the accounts of operatives arrested so far, the Emni has become the crucial cog in the group’s terrorism machinery, and its trainees led the Paris attacks and built the suitcase bombs used in a Brussels airport terminal and subway station. Investigation records show that its foot soldiers have also been sent to Austria, Germany, Spain, Lebanon, Tunisia, Bangladesh, Indonesia and Malaysia.

With European officials stretched by a string of assaults by seemingly unconnected attackers who pledged allegiance to the ISIS, also known as ISIL, Mr. Sarfo suggested that there may be more of a link than the authorities yet know. He said he was told that undercover operatives in Europe used new converts as go-betweens, or “clean men,” who help link up people interested in carrying out attacks with operatives who can pass on instructions on everything from how to make a suicide vest to how to credit their violence to ISIS.

The group has sent “hundreds of operatives” back to the European Union, with “hundreds more in Turkey alone,” according to a senior United States intelligence official and a senior American defense official, both of whom spoke on the condition of anonymity to discuss intelligence.

Mr. Sarfo, who was recently moved out of solitary confinement at his German prison because he is no longer considered violent, agrees with that assessment. “Many of them have returned,” he said. “Hundreds, definitely.”

Vetting Recruits

The first port of call for new arrivals to ISIS is a network of dormitories in Syria, just across the border from Turkey. There, recruits are interviewed and inventoried.

Mr. Sarfo was fingerprinted, and a doctor came to draw a blood sample and perform a physical examination. A man with a laptop conducted an intake interview. “He was asking normal questions like: ‘What’s your name? What’s your second name? Who’s your mom? Where’s your mom originally from? What did you study? What degree do you have? What’s your ambition? What do you want to become?’” Mr. Sarfo said.

His background was also of interest. He was a regular at a radical mosque in Bremen that had already sent about 20 members to Syria, at least four of whom were killed in battle, according to Daniel Heinke, the German Interior Ministry’s counterterrorism coordinator for the area. And he had served a one-year prison sentence for breaking into a supermarket safe and stealing 23,000 euros. Even though the punishment for theft in areas under ISIS control is amputation, a criminal past can be a valued asset, Mr. Sarfo said, “especially if they know you have ties to organized crime and they know you can get fake IDs, or they know you have contact men in Europe who can smuggle you into the European Union.”

The bureaucratic nature of the intake procedure was recently confirmed by American officials after USB drives were recovered in the recently liberated Syrian city of Manbij, one of the hubs for processing foreign fighters.

Mr. Sarfo checked all the necessary boxes, and on the third day after his arrival, the members of the Emni came to ask for him. He wanted to fight in Syria and Iraq, but the masked operatives explained that they had a vexing problem.

“They told me that there aren’t many people in Germany who are willing to do the job,” Mr. Sarfo said soon after his arrest last year, according to the transcript of his interrogation by German officials, which runs more than 500 pages. “They said they had some in the beginning. But one after another, you could say, they chickened out, because they got scared — cold feet. Same in England.”

By contrast, the group had more than enough volunteers for France. “My friend asked them about France,” Mr. Sarfo said. “And they started laughing. But really serious laughing, with tears in their eyes. They said, ‘Don’t worry about France.’ ‘Mafi mushkilah’ — in Arabic, it means ‘no problem.’” That conversation took place in April 2015, seven months before the coordinated killings in Paris in November, the worst terrorist attack in Europe in over a decade.

While some details of Mr. Sarfo’s account cannot be verified, his statements track with what other recruits related in their interrogations. And both prison officials and the German intelligence agents who debriefed Mr. Sarfo after his arrest said they found him credible.

Since the rise of ISIS over two years ago, intelligence agencies have been collecting nuggets on the Emni. Originally, the unit was tasked with policing ISIS’ members, including conducting interrogations and ferreting out spies, according to interrogation records and analysts. But French members arrested in 2014 and 2015 explained that the Emni had taken on a new portfolio: projecting terror abroad.

“It’s the Emni that ensures the internal security inside Dawla” — the Arabic word for state — “and oversees external security by sending abroad people they recruited, or else sending individuals to carry out violent acts, like what happened in Tunisia inside the museum in Tunis, or else the aborted plot in Belgium,” said Nicolas Moreau, 32, a French citizen who was arrested last year after leaving ISIS in Syria, according to his statement to France’s domestic intelligence agency.

Mr. Moreau explained that he had run a restaurant in Raqqa, Syria, the de facto capital of the group’s territory, where he had served meals to key members of the Emni — including Abdelhamid Abaaoud, the on-the-ground commander of the Paris attacks, who was killed in a standoff with the police days later.

Other interrogations, as well as Mr. Sarfo’s account, have led investigators to conclude that the Emni also trained and dispatched the gunman who opened fire on a beach in Sousse, Tunisia, in June, and the man who prepared the Brussels airport bombs.

Records from French, Austrian and Belgian intelligence agencies show that at least 28 operatives recruited by the Emni succeeded in deploying to countries outside of the ISIS’ core territory, mounting both successful attacks and plots that were foiled. Officials say that dozens of other operatives have slipped through and formed sleeper cells.

In his own interactions with the Emni, Mr. Sarfo realized that they were preparing a global portfolio of terrorists and looking to fill holes in their international network, he said.

He described what he had been told about the group’s work to build an infrastructure in Bangladesh. There, a siege by a team of Islamic State gunmen left at least 20 hostages dead at a cafe last month, almost all of them foreigners.

Mr. Sarfo said that for Asian recruits, the group was looking specifically for militants who had emerged from Al Qaeda’s network in the region. “People especially from Bangladesh, Malaysia and Indonesia — they have people who used to work for Al Qaeda, and once they joined ISIS, they are asking them questions about their experiences and if they have contacts,” he said.

(The New York Times)