Four men have been charged with terrorism over last week's attack at a concert hall near Moscow that killed more than 130 people. Russian media have identified the suspects as Tajik nationals.

Local media outlets report they are in their teens to their 30s. Russia's Interfax news agency says the four have lived in Russia.

Tajikistan is a former Soviet Union republic. Many Tajikis who are suffering from poverty go to Russia to work. Weapons and drugs have been smuggled from neighboring Afghanistan. Violent incidents allegedly related to the Islamic State group have happened in Tajikistan.

The Amaq news agency, which is linked to the group, reported the attack was carried out by Islamic State militants.

On Friday, gunmen opened fire on concertgoers in the city of Krasnogorsk, northwest of Moscow. At least 137 people have been confirmed dead and 182 were wounded.

Russian authorities have detained 11 people, including four said to be directly involved in the attack. A Moscow court says two of them have admitted to the charges.

President Vladimir Putin has claimed that Ukraine is to blame for the attack. Ukrainian President Volodymyr Zelenskyy denies any involvement.

US Vice President Kamala Harris also denies the country was responsible. She said, "What we know to be the case is that ISIS-K is actually, by all accounts, responsible for what happened."

ISIS-K is a regional Islamic State group based in Afghanistan. The group allegedly staged a suicide attack in front of the Russian Embassy in Kabul in 2022.

ISIS-K has long regarded the Putin administration as an enemy. While the group was trying to expand its base in the Middle East, Russia joined the US-led coalition's attacks on the group. The air strikes weakened the group and helped make it lose its footholds.