Article: The Islamic State group, also known as ISIS, has claimed responsibility for the horrific terrorist attack on a concert venue in Moscow, which left at least 137 people dead and more than 100 injured. The attack, considered Russia's worst in decades, was carried out by gunmen affiliated with ISIS-K, an ISIS affiliate that operates in central Asia.

Russian authorities have accused four men from Tajikistan of being behind the assault and charged them with committing a terrorist act. These suspects appeared in court in Moscow on Sunday and have been remanded into pre-trial detention until May 22nd.

US officials have linked the attack to ISIS-K, an ISIS branch formed in 2015 and active in Afghanistan, Pakistan, and Iran. The group has gained notoriety as one of the world's deadliest terror organizations, ranking fourth in 2018, according to the Institute for Economics and Peace.

Since November, the United States has been receiving intelligence that ISIS-K intended to carry out an attack in Russia and had shared these warnings with Moscow. US Vice President Kamala Harris confirmed that ISIS-K was responsible for the Moscow concert attack.

ISIS-K aims to establish a "pure Islamic state" through a global transnational caliphate governed by Sharia law. The group has shown enmity towards Russia, in part due to historical grievances. Russian involvement in the Syrian civil war, brutal tactics in the Chechen wars, and scorched-earth policies in the Caucasus have made Russia a target for ISIS's animosity.

This attack in Moscow follows ISIS-K's globally consequential action in August 2021 - a bombing outside Kabul airport that killed 13 US military personnel and 170 Afghans. This event drew a promise of retribution from US President Joe Biden.

In Afghanistan, ISIS-K remains active and responsible for numerous devastating attacks, including the Kabul airport blast and attacks on Kabul University and a girls' high school. The group's presence in Afghanistan has raised concerns that it could pose a major threat not only in the region but also in Europe and Asia.

The United Nations estimates that ISIS-K has up to 2,200 core fighters based in Kunar and Nangarhar provinces of Afghanistan. Despite the Taliban's takeover of Afghanistan and the withdrawal of US troops, ISIS-K continues to plan attacks, maintaining its status as the most active terror group in the country.

The trial of the four Tajik suspects in the Moscow concert attack will shed more light on the connections and operations of ISIS-K. As the world continues to grapple with the threat posed by ISIS and its affiliates, international cooperation and intelligence sharing remain crucial to combatting terrorism and ensuring the safety of innocent lives.