ISIS-K a major terrorist threat to Europe amid foiled concert attack: UN official

The United Nations counterterrorism chief said Europe faces a more acute threat from ISIS-K, the Islamic State affiliate to whom a 19-year old man pledged allegiance before plotting to terrorize Taylor Swift's concertgoers in Vienna this week .

Vladimir Vorokov, the UN undersecretary for counterterrorism, said Thursday the ISIS-K threat, "regrettably," has "become manifest" in Vienna, where three of Swift's concerts were canceled when Austrian authorities arrested three suspects , and that the ISIS satellite is increasing in strength and influence.

"The group is considered the greatest external terrorist threat to the continent," Vorokov told the UN Security Council, citing its "intensified" recruitment efforts and array of financial and logistical nodes.

Terrorists from the ISIS-K group, based in Afghanistan and named after the Khorasan region that includes parts of Central and South Asia, killed at least140 people in a Moscow concert venue in March and over 100 in bombings in Iran in January.

It is "the most complex, dynamic and, quite frankly, dangerous threat environment that I've experienced in the 40 plus years that I've been involved in law enforcement and homeland security," John Cohen, ABC News contributor and former acting undersecretary for intelligence at the US Department of Homeland Security, said.

The foiled attacks in Vienna fit two patterns around extremist ideology affecting the European continent, said Lorenzo Vidino, director of the George Washington University's Program on Extremism.

Would-be attackers are younger, ranging from as young as 13, 14, and 15 years old -- "a teenage dominated scene," Vidino told ABC News. The those arrested in connection with the Swift concert plot are 17, 18 and 19 years old, authorities have said.

"It's a much more unstructured scene in which you have people who self-radicalize and sort of come together on online platforms, sometimes also offline. But the online component is getting bigger over the last few years, and they activate themselves independently," Vidino said.

The second dynamic has been the emergence of ISIS-K as the terrorist organization's strongest arm, Vidino said.

"[ISIS] mostly operates through branches in different parts of the world, and the one that I would say is the most successful -- and arguably the only one that has been consistently operating also in the West and planning terrorist attacks in the West -- is ISIS-K," he said.

Austrian authorities said suspects were radicalized online and that chemical substances and technical devices were found at the 19-year-old's home.

He was "clearly radicalized in the direction of the Islamic State and thinks it is right to kill infidels," Omar Haijawi-Pirchner, head of Austria's Directorate of State Security and Intelligence, said Thursday.

Increasing numbers of young people are streaming ISIS and al-Qaeda videos, leading to radicalization, Haijawi-Pirchner added.

ABC News reported Wednesday, when the three Swift concerts were canceled after the arrests, that US intelligence found the pledge to ISIS-K by at least one of the suspects in early July on the messaging app Telegram.

Multiple sources told ABC News that the U.S. passed the original intelligence of a terror threat to Austria. It's not the first time the U.S. has passed along this kind of information. Ahead of the Moscow attack in March, the State Department had issued public warnings to Americans in Russia to avoid large gatherings.

"When it comes to the [foiled] plots in Europe, I would say the vast majority of them were triggered by intelligence coming from the U.S.," Vidino said.

Cohen, a former counterterrorism coordinator at DHS, said the Vienna plot "is consistent with what has concerned law enforcement and security officials over the past several years."

Terrorists have learned to "leverage the power of the internet to spread content that's specifically intended to inspire and inform terrorist attacks across Europe and the United States," Cohen said.

ISIS controlled significant territory in Syria and Iraq and governed according to its radical ideology, ruling over as many as 12 million people by the end of 2015. That footprint had reduced significantly by 2019 after American and allied counterinsurgency operations in the region.

"What they figured out is that the United States has become very effective at detecting terrorist travel and intercepting terrorist communications, and therefore very adept at … identifying terrorist leaders," Cohen said of ISIS. "So they shifted their tactics, and they added to their playbook the spreading of online content in an effort to influence the behavior of disaffected, angry young people across the globe."

That "highly sophisticated media operation," Cohen said, has continued to prove a potent force, particularly in empowering the regional arteries that run to a center largely devoid of the conventional capabilities ISIS had in Syria and Iraq a decade ago.