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.

As the world absorbs the horror of the ISIS-K slaughter inside a Russian concert hall, prominent members of Congress are warning the Afghan-based terror group could strike inside the United States.

House Foreign Affairs Committee Chairman Mike McCaul said Sunday the threat of an attack was heightened by President Joe Biden‘s bungled withdrawal from Afghanistan, which gave ISIS-K  a breeding ground to train and carry out attacks.

Five years ago this month, an American-backed Kurdish and Arab militia ousted Islamic State fighters from a village in eastern Syria, the group’s last sliver of territory.

Since then, the organization that once staked out a self-proclaimed caliphate across Iraq and Syria has metastasized into a more traditional terrorist group — a clandestine network of cells from West Africa to Southeast Asia engaged in guerrilla attacks, bombings and targeted assassinations.