The US has intelligence confirming the self-proclaimed Islamic State's (IS) claim of responsibility for a at a concert near Moscow on Friday, a US official has told Reuters.
While Friday's attack in Russia was a dramatic escalation, experts say the group has opposed Russian President Vladimir Putin in recent years.
Here's some information about the Afghan IS branch known as ISIS-K and its motives for attacking Russia.
What is IS-K?
The attack was claimed by an Afghan branch of IS known as ISIS-K or IS-K.
Islamic State Khorasan (IS-K) — named after an old term for the region that included parts of Iran, Turkmenistan and Afghanistan — emerged in eastern Afghanistan a decade ago.
Months after IS declared a caliphate in Iraq and Syria in 2014, breakaway fighters from the Pakistani Taliban joined militants in Afghanistan to form a regional chapter, pledging allegiance to IS leader Abu Bakr al-Baghdadi.
The group was formally acknowledged by the central IS leadership the next year as it sunk roots in northeastern Afghanistan, particularly Kunar, Nangarhar and Nuristan provinces.
It quickly established a reputation for extreme brutality.
Although it is one of the most active regional affiliates of IS, the group has seen its membership decline since peaking around 2018. The Taliban and US forces inflicted heavy losses.
The United States has said its ability to develop intelligence against extremist groups in Afghanistan such as IS-K has been reduced since the withdrawal of US troops from the country in 2021.
What attacks have the group carried out in the past?
IS-K has a history of attacks, including against mosques, inside and outside Afghanistan. It has especially targeted Muslims from sects it considers heretical, including Shiites.
Earlier this year, the US intercepted communications confirming the group carried out .
In September 2022, IS-K militants claimed responsibility for a deadly suicide bombing at the Russian embassy in Kabul.
The group was responsible for an attack on Kabul's international airport in 2021 that killed 13 US troops and scores of civilians during the chaotic US evacuation from the country.
Earlier this month, the top US general in the Middle East said IS-K could attack US and Western interests outside of Afghanistan "in as little as six months and with little to no warning".
Why would IS-K attack Russia?
"IS-K has been fixated on Russia for the past two years, frequently criticizing Putin in its propaganda," said Colin Clarke of Soufan Center, a Washington-based research group.
Michael Kugelman of the Washington-based Wilson Center said that IS-K "sees Russia as being complicit in activities that regularly oppress Muslims".
Putin's support of Syrian President Bashar al-Assad was instrumental in turning the tide of the Syrian war against IS and claiming back vast swathes of the country that the militant group was holding by 2013.
IS-K also counts as members a number of Central Asian militants with their own grievances against Moscow, Kugelman added.
