Russian authorities have arrested 11 people in connection with one horrific attack in a crowded concert hall near Moscow as the death toll rose to 115 and more than 120 people were injured.

On Saturday, the Russian Investigative Committee said more bodies had been found at the Crocus town hall in the northern Moscow suburb of Krasnogorsk.

Moscow Region Governor Andrei Vorobyov, who visited the venue on Saturday, said: “As for the dead, I must say right away that the number of victims will increase significantly.”

Armed men wear combat fatigues open fire with automatic weapons at the venue on Friday as concertgoers prepared for a performance by Picnic, a veteran Soviet-era rock band.

An affiliate of ISIL (ISIS), Islamic State Khorasan Province (ISIS-K), who was active in Afghanistan and Iran, claimed responsibility for the attack.

Authorities have yet to officially say who carried out the deadliest attack in Russia in at least a decade. In 2004, more than 330 people, half of them children, were killed Beslan school wins.

ISIS-K, that previously targeted The Russian embassy in Kabul claimed its fighters attacked “a large gathering” on the outskirts of Moscow and “safely returned to their bases.”

Federal Security Service (FSB) chief Alexander Bortnikov reported to President Vladimir Putin that those arrested early Saturday included four gunmen and that investigations to identify their accomplices were continuing.

People died from gunshot wounds and smoke inhalation after a fire ripped through the 6,000-seat venue, according to the investigative committee.

“The terrorists used a flammable liquid to set fire to the grounds of the concert hall where spectators, including the wounded, were staying,” it said.

According to the Russian Emergencies Ministry, around 107 people were still in hospital on Saturday morning.

A confirmed video showed people taking their seats in the hall and then rushing for the exits as repeated gunfire echoed over screams. Other footage showed men shooting at groups of people. Some victims lay motionless in pools of blood.

“Suddenly there was a bang behind us – shots. A gunshot – I don’t know what,” a witness, who did not want to be named, told Reuters.

“Mass panic began. “Everyone ran to the escalator,” the witness said. “Everyone was screaming; everyone was running.”

Russian officials said security had been tightened at Moscow’s airports, train stations and subway system. The mayor canceled all mass gatherings, while theaters and museums in the area, home to more than 12 million people, were ordered to remain closed for the weekend. Other Russian regions also tightened security precautions.

Russian politician Alexander Chinschtein said the attackers fled in a Renault vehicle spotted by police on Friday evening in the Bryansk region, about 340 km (210 miles) southwest of Moscow, and ignored requests to stop.

He said two people were arrested after a chase and two others fled into a forest. The Kremlin report shows that they, too, were later arrested.

Khinshtein said a pistol, a magazine for an assault rifle and passports from Tajikistan – a Central Asian nation that was formerly part of the Soviet Union – were found in the car.

ISIL involvement

Russian authorities called it a “terrorist attack” but did not comment on ISIS’s claims.

Murat Aslan, a retired Turkish army colonel and military analyst, said ISIS-K has global targets, not just Central Asia.

“They used to be in Iran. Now they are in Moscow,” Aslan told Al Jazeera. “We will likely see more attacks in other capitals.”

Aslan said the group likely targeted Moscow in part because of Russia’s intervention in Syria, where Moscow has supported President Bashar al-Assad against ISIL. “[ISIS-K] “Consider such countries as hostile,” Aslan said.

The attack highlights how ISIL and ISIS-K have gained strength because of their ideological reach, said Kabir Taneja, a fellow at the New Delhi-based think tank Observer Research Foundation and author of “The ISIS Peril.”

“ISIS-K in Afghanistan has significantly increased in strength,” Taneja told Al Jazeera. “And not just ISIS-K, ISIL is also experiencing an increase in operational capabilities in its original areas of operation in Syria and Iraq.”

“ISIL today successfully operates in a form of silence in which it is ideologically powerful, even if it is no longer as politically, tactically or strategically powerful,” he said.

Andrei Kartapolov, a lawmaker and former general, said Russia should retaliate on the battlefield if Ukraine was involved in the Moscow attack, Russian news agency RIA Novosti reported.

The FSB claimed the perpetrators were on their way to the border with Ukraine when they were arrested, Russian news agency Interfax reported, adding that the suspects had “contacts” within Ukraine.

Ukrainian presidential adviser Mykhaylo Podolyak said: “It makes no sense at all. Ukraine has never resorted to terrorist methods.”

He posted on

We expected the version of Russian officials about the “Ukrainian trace” in the terrorist attack in the year #CrocusCityHall. Primitivism and predictability are ideal characteristics of the Russian security services. Once again, the #FSB confirms this … But it is still necessary to emphasize that …

— Mykhailo Podolyak (@Podolyak_M) March 23, 2024

Three days before the attack, Putin publicly dismissed Western warnings of an impending attack in Moscow as propaganda aimed at intimidating Russian citizens.

The White House said it received information earlier this month about a “planned terrorist attack” in Moscow – “potentially targeting large gatherings, including concerts” – and forwarded the information to Moscow.

This was under its “duty to alert” policy, under which the US alerts nations or groups when it receives information about specific threats to kidnap or kill multiple victims, said Adrienne Watson, spokeswoman for the National Security Council.

Earlier this month, the U.S. government had information about a planned terrorist attack in Moscow that may have targeted large gatherings and concerts, prompting the State Department to issue a public warning to Americans in Russia.

— Adrienne Watson (@NSC_Spox) March 23, 2024

A Russian security source confirmed receiving the warning from the US and said the information contained “no details,” RIA Novosti reported.

The attack sparked condemnation and shock from world leaders and the United Nations Security Council “strongly condemned the heinous and cowardly terrorist attack.”