Explainer: Why did ISIS-K attack a Moscow theater?

WASHINGTON, March 22 (Reuters) - 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:

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.