The U.S. has intelligence confirming Islamic State's claim of responsibility for a deadly shooting attack at a concert near Moscow on Friday, a U.S. official told Reuters.

Here is information about the Islamic State's Afghan branch known as ISIS-K and their motives for attacking Russia:

WHAT IS ISIS-K?

Islamic State Khorasan (ISIS-K), named after an old term for the region that included parts of Iran, Turkmenistan and Afghanistan, emerged in eastern Afghanistan in late 2014 and quickly established a reputation for extreme brutality.

One of the most active regional affiliates of the Islamic State militant group, ISIS-K has seen its membership decline since peaking around 2018. The Taliban and U.S. forces inflicted heavy losses.

The United States has said its ability to develop intelligence against extremist groups in Afghanistan such as ISIS-K has been reduced since the withdrawal of U.S. troops from the country in 2021.

WHAT ATTACKS HAS THE GROUP CARRIED OUT?

ISIS-K has a history of attacks, including against mosques, inside and outside Afghanistan.

Earlier this year, the U.S. intercepted communications confirming the group carried out twin bombings in Iran that killed nearly 100 people.

In September 2022, ISIS-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 U.S. troops and scores of civilians during the chaotic U.S. evacuation from the country.

Earlier this month, the top U.S. general in the Middle East said ISIS-K could attack U.S. and Western interests outside of Afghanistan "in as little as six months and with little to no warning."

WHY WOULD THEY ATTACK RUSSIA?

While the attack by ISIS-K in Russia on Friday was a dramatic escalation, experts said the group has opposed Russian President Vladimir Putin in recent years.

"ISIS-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 ISIS-K "sees Russia as being complicit in activities that regularly oppress Muslims."

He added that the group also counts as members a number of Central Asian militants with their own grievances against Moscow.