Russian President Vladimir Putin has announced the apprehension of all four assailants responsible for a tragic assault at a crowded concert venue in Moscow.

The harrowing incident resulted in the death of at least 133 individuals, with over 140 sustaining injuries as the attackers invaded the premises, firing indiscriminately and setting the establishment ablaze.

Authorities disclosed a total of 11 detentions, with the four gunmen intercepted en route to Ukraine.

The Islamic State (IS) group has claimed responsibility for the attack.

On Saturday, the IS-affiliated Amaq channel on Telegram shared an image purportedly depicting the four masked perpetrators. Russia has yet to officially address the IS assertion.

Subsequently, the group circulated distressing footage of the assault, confirmed as authentic by the BBC. The network has opted not to air the graphic video.

In a televised statement, President Putin denounced the massacre — the deadliest in Russia in nearly two decades — condemning it as a "barbaric terrorist act." He echoed prior statements from Russian security services suggesting the assailants' attempted flight to Ukraine.

Kyiv swiftly rebuffed allegations of involvement in the attack as "absurd."

Andriy Yusov, a spokesperson for the Ukrainian military intelligence directorate, dismissed claims that the suspects were headed to Ukraine, deeming it illogical and suicidal.

Ukrainian President Volodymyr Zelensky accused President Putin of attempting to shift blame onto Ukraine for the atrocity. Zelensky criticized Putin for his silence following the incident, accusing him of plotting to implicate Ukraine.

The US National Security Council disclosed having cautioned Russia about potential attacks on "large gatherings," including concerts, in Moscow earlier in the month. The Kremlin dismissed this as "propaganda" and an effort by Washington to interfere in recent Russian elections.

On Saturday, the White House said it condemned the "heinous" attack and described Islamic State as "a common terrorist enemy that must be defeated everywhere".

Reports of a serious attack inside the Crocus City Hall, in Moscow's Krasnogorsk suburb, began arriving at around 20:00 local time (17:00 GMT) on Friday.

Up to 6,200 people were gathered there for a Friday night rock concert by veteran band Picnic when the shooting started.

One video posted online showed several men striding across the concourse, where they opened fire at members of the public, before rearming and entering the hall.

Crowds of people were filmed screaming and running in panic as the men burst in. Others were seen taking cover behind their seats as the men fired into the auditorium.

Some of those who tried to escape from the gunmen were thought to have fled to the basement, and others to the roof.

"They were just walking and gunning down everyone methodically in silence. Sound was echoing and we could not understand what was where," concertgoer Anastasia Rodionova recalled.

Vitaly, another visitor, saw the attack unfolding from a balcony. "They threw some petrol bombs, everything started burning," he said.

Outside the hall, huge plumes of smoke filled the sky. A fire was later seen engulfing the hall's roof and facade. Tass state news agency reported that around a third of the building had been set alight.

Other reports spoke of explosions, the force of which shattered the glass on the top two floors of the structure.

A number of special forces units stormed the venue, while medical personnel, and dozens of ambulances were sent to the scene. Helicopters, circling overhead, tried to douse the fire.

The Russian Investigative Committee said that the attackers used flammable liquid to set fire to sections of the concert hall and that the deaths of the victims were caused by gunshot wounds and poisoning by combustion products.

On Saturday, a makeshift memorial was set up outside the concert hall where Muscovites lit candles and laid flowers. Others queued to donate blood for the victims of the massacre.

In Moscow and other towns and cities, electronic billboards displayed the image of a single burning candle and the word "Skorbim" - "we mourn."

President Putin has declared Sunday to be a day of national mourning and weekend events have been cancelled across Russia.

Memorials also appeared outside Russian embassies in several countries, including the UK.

Semyon Khraptsov, whose wife attended the concert last night and is now missing, said he had tried calling five hospitals but the phone lines were all busy.

"I am in complete panic. I don't know what to do, [I'm in] complete hopelessness," he said.

OK