This grab taken from a UGC video shows gunmen shooting in a concert hall in Krasnogorsk, western edge of Moscow region, Russia, March 22, 2024. (ASTRA VIA AP)

MOSCOW – Russia has arrested 11 people including four suspected gunmen in connection with a shooting rampage that killed 93 people in a concert hall near Moscow, the Kremlin said on Saturday.

It said FSB security service chief Alexander Bortnikov had reported to President Vladimir Putin that those detained included "four terrorists" and that the service was working to identify their accomplices.

Russia's Investigative Committee said the death toll had leapt to 93 from the attack in which camouflage-clad gunmen opened fire with automatic weapons at concertgoers near the capital on Friday. 

It said some died from gunshot wounds and others in a huge fire that broke out in the complex.

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Interfax quoted the FSB security service as saying the four suspected gunmen had been arrested while heading to the Ukrainian border, and that they had contacts in Ukraine. It said they were being transferred to Moscow.

Russia has not made public any evidence of a Ukrainian connection. Ukrainian presidential adviser Mykhailo Podolyak said on Friday that Kyiv had nothing to do with Friday's attack, for which the Islamic State group claimed responsibility.

Russian lawmaker Alexander Khinshtein said the attackers had fled in a Renault vehicle that was spotted by police in Bryansk region, about 340 km southwest of Moscow on Friday night and disobeyed instructions to stop.

He said two were arrested after a car chase and two others fled into a forest. From the Kremlin account, it appeared they too were later detained.

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Khinshtein said a pistol, a magazine for an assault rifle, and passports from Tajikistan were found in the car. Tajikistan is a mainly Muslim Central Asian state that used to be part of the Soviet Union.

Russian Rosguardia (National Guard) servicemen secure an area at the Crocus City Hall on the western edge of Moscow, Russia, March 23, 2024. (MOSCOW NEWS AGENCY VIA AP)

Gunfire and screams

The shooting took place on Friday evening at Crocus City Hall, a concert venue just west of Moscow where a Soviet-era rock band was due to perform.

Verified video showed people taking their seats in the hall, then rushing for the exits as repeated gunfire echoed above screams. Other video showed men shooting at groups of people. Some victims lay motionless in pools of blood.

"Suddenly there were bangs behind us - shots. A burst of firing - I do not know what," one witness, who asked not to be identified by name, told Reuters.

Long lines formed in Moscow on Saturday for people to donate blood. Health officials said more than 120 people were wounded.

Medics transport the body of a victim in a waiting ambulance near the burning building of the Crocus City Hall on the western edge of Moscow, Russia, March 22, 2024. (MOSCOW NEWS AGENCY VIA AP)

"The death toll is expected to rise," the Investigative Committee, which handles major crimes in Russia, said on Telegram.

The Moscow city and regional governments said they would provide financial support for families of the victims and those injured, as well as paying for funerals.

Islamic State, the militant group that once sought control over swathes of Iraq and Syria, claimed responsibility for the attack, the group's Amaq agency said on Telegram.

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Islamic State said its fighters attacked on the outskirts of Moscow, "killing and wounding hundreds and causing great destruction to the place before they withdrew to their bases safely". The statement gave no further detail.

The US has intelligence confirming Islamic State's claim of responsibility for the shooting, a US official said on Friday. The official said Washington had warned Moscow in recent weeks of the possibility of an attack.

In this photo taken from a video released by the Investigative Committee of Russia on March 23, 2024, a Kalashnikov assault rifle lies on the ground as Investigators from the Investigative Committee of Russia together with the operational units of the Ministry of Internal Affairs and the FSB, work at the scene after a terrorist attack on the building of the Crocus City Hall on the western edge of Moscow, Russia. (INVESTIGATIVE COMMITTEE OF RUSSIA VIA AP)

"We did warn the Russians appropriately," said the official, speaking on condition of anonymity, without providing any additional details.

The attack on Crocus City Hall, about 20 km from the Kremlin, happened two weeks after the US embassy in Russia warned that "extremists" had imminent plans for an attack in Moscow.

People light candles in memory of the victims of the terrorist attack in Moscow, in the center of in the center of Simferopol, in Russian-held Crimea, Friday, March 22, 2024. (PHOTO / AP)

Hours before the embassy warning, the FSB said it had foiled an attack on a Moscow synagogue by Islamic State's affiliate in Afghanistan, known as ISIS-Khorasan or ISIS-K, which seeks a caliphate across Afghanistan, Pakistan, Turkmenistan, Tajikistan, Uzbekistan and Iran.

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Putin changed the course of the Syrian civil war by intervening in 2015, supporting President Bashar al-Assad against the opposition and Islamic State.

The broader Islamic State group has claimed deadly attacks across the Middle East, Afghanistan, Pakistan, Iran, Europe, the Philippines, and Sri Lanka.

In this photo released by the Russian Emergency Ministry Press Service on March 23, 2024, Russian Emergency Ministry rescuers work inside the Crocus City Hall on the western edge of Moscow, Russia, following an attack the previous day. (RUSSIAN EMERGENCY MINISTRY PRESS SERVICE VIA AP)

Russian Foreign Ministry spokeswoman Maria Zakharova said it was a "bloody terrorist attack" that the world should condemn.

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The US, European and Arab powers and many former Soviet republics expressed shock and sent their condolences. The United Nations Security Council condemned what it called a "heinous and cowardly terrorist attack".

Russia tightened security at airports, transport hubs and across the capital – a vast urban area of over 21 million people. All large-scale public events were cancelled across the country.