(Bloomberg) -- Western publics may have assumed that Islamic State was yesterday’s problem after the US and its allies smashed the group’s attempt to establish a caliphate in parts of Iraq and Syria. Now, the violently Islamist organization looks to be mutating into a pernicious new threat.

Islamic State claimed responsibility for Friday’s assault on a concert hall in Moscow that killed at least 137 people, the deadliest attack in the Russian capital since 2002. Russian President Vladimir Putin dismissed a public warning issued by US officials who pointed to a branch known as ISIS-K, and he instead sought to divert public attention toward Kyiv.

“Putin has taken his eye off the ball because of the war in Ukraine,” Alex Younger, former head of MI6, Britain’s foreign security agency, said in an interview. While the West has been lucky to avoid a series of attacks, “the threat has never gone away,” he said.

That’s a grim reality not just for Russia, but for western Europe as it prepares to host major sporting events including the Olympics this summer. The threat of a resurgence of Islamist terror in the West may also play into a charged US presidential campaign in which foreign affairs looks set to feature more prominently than usual.  

US Director of National Intelligence Avril Haines told a senate hearing in March that ISIS “remains a significant counterterrorism concern.”

Paris Olympics 

The bloodshed in Moscow rammed that message home, and is prompting governments to reassess threat levels that were already under review due to the Israel-Hamas war. 

France raised its security alert to the maximum months before hosting the 2024 Summer Olympics. President Emmanuel Macron said the decision was triggered by “credible and solid information,” and that ISIS-K had attempted several attacks on French soil in recent months. 

Paris has its own bitter experience of a jihadist attack on a concert hall, after the 2015 assault on the Bataclan and other sites in the city that killed 130 people.

Germany, which will host the Euro 2024 football championships from June, sees the terror threat as “acute,” Interior Minister Nancy Faeser told the newspaper Sueddeutsche Zeitung. Only last week, two suspected Islamic State members were arrested in the eastern German state of Thueringen on suspicion of plotting an attack on the Swedish parliament.

The UK has repeatedly warned of and discussed with partners the increased threat from ISIS-K in recent months, an official said. The Netherlands raised its threat level to “substantial” in December, warning of “risks posed by radicalized individuals” inspired by terrorist organizations.

Like its parent body that flourished in Syria during the civil war’s onset a decade ago, ISIS-K emerged as a force in Afghanistan following the chaotic US withdrawal of 2021. The K stands for Khorasan, the ancient name for a part of the world that extends from Afghanistan into areas of Pakistan and the central Asian states of Russia’s former Soviet backyard.

That includes Tajikistan, where four suspects arrested over the Moscow attack are from. The mountainous republic of 10 million is central Asia’s poorest state and has struggled for years against Islamist insurgents challenging its longstanding autocratic ruler Emomali Rahmon.

Russia has an army base in Tajikistan that it reinforced to “counter the terrorist threat” after the US left Afghanistan to the Taliban. Other central Asian states including Kazakhstan have also battled attacks by Islamist militants in recent years.

A January United Nations report on the global ISIS threat said ISIS-K had been actively recruiting in Tajikistan recently by focusing on attracting disillusioned Taliban and foreign fighters. ISIS and its affiliates “retained their capacity to conduct terrorist attacks and project a threat beyond their areas of operations,” the report said.

Yet when the US warned about the potential threat of an attack in Moscow, saying it alerted Russian officials, the information seems not to have been acted upon. Indeed, three days before the assault, Putin dismissed the warning as a western attempt “to intimidate and destabilize our society.”

That disregard underlined the almost complete breakdown in trust between Russia and the West since Putin ordered the February 2022 invasion of Ukraine. The lack of coordination is creating holes in the security environment for organizations like ISIS-K to exploit through attacks aimed at raising their profile and boosting recruitment.

ISIS-K is believed to be behind deadly bombings in Iran on Jan. 3 that killed almost 100 people near the grave of Iranian commander Qassem Soleimani. The strikes by the extremist Sunni group, which is ideologically opposed to Shia-dominated Iran, threatened to further inflame Middle East tensions that were already surging over the war in Gaza.

For foreign policy observers, the rise of ISIS-K is a reminder of the unintended consequences of President Joe Biden’s decision to pull American forces from Afghanistan — ending its longest war — more than 20 years after the Sept. 11 attacks led to US military intervention with the aim of eradicating jihadist terrorism. The threat was never vanquished, but rather morphed into different strains.

House Republicans are leading an investigation into the manner of the withdrawal and plan to release a final report in the summer that’s likely to be highly critical. At the same time, Biden’s Republican rival Donald Trump has long argued for a return to isolationism that may prove hard to sustain in the face of a renewed terrorist threat. 

As Christine Abizaid, the director of the US National Counterterrorism Center, told Congress last year: ISIS-K is the “threat actor I am most concerned about.”

--With assistance from Ania Nussbaum, Samy Adghirni, Kitty Donaldson and Alex Wickham.

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