Videos circulated online picture three different men allegedly being detained by a group of soldiers and claiming they were paid to carry out the attack as ISIS takes responsibility.

One suspect can be seen barefoot with his arms and legs tied together while blood pours from the forehead of the second suspect. Another suspect is shown shaking on his knees as he apparently confesses to carrying out the mass shooting, which left at least 133 people dead.

“I was listening to a preacher’s teaching on Telegram” the suspect answers in response to a soldier’s interrogation.

“His assistant wrote to me telling me to kill people,” he continues.

“I don’t know (his name). No first name, no last name, no nothing. They only wrote to me about a month ago.

“He wrote that he promised me about one million roubles.”

The suspect was reportedly filmed while being held in the Bryansk region in western Russia and told authorities his name was Fariduni Shamsidin.

The man allegedly goes on to say he was told to walk into the venue and kill anyone after he had flown from Turkey on March 4 and received instructions from unknown people via Telegram to carry out the attack in exchange for $16,612 (₽1,000,000).

Another suspect allegedly said he had been promised $8328 (₽500,000) and had received $4164 (₽250,000) in an advance payment.

According to local reports, the group of suspects were travelling to Ukraine when they were reportedly caught by Chechen fighters loyal to Putin.

Russian media previously shared photographs of the four suspected “terrorists” and named the men as Makhmadrasul Nasridinov, 27, Rivozhidin Ismonov, 51, Shokhindzhonn Safolzoda, 21, and Rustam Nazarov, 29

Russia has now arrested 11 people, including the four “terrorists” directly involved in the deadly attack on a Moscow concert hall, Russian news agencies have reported.

The head of Russia’s Federal Security Service (FSB) reportedly informed Russian President Vladimir Putin “about the detention of 11 people” after gunmen stormed the Crocus Hall and began shooting people inside on Friday night local time. At least 133 people were killed, and another 145 are understood to have been injured.

According to the Russian government, the four suspected gunmen arrested are not Russian citizens.

“They are all foreign nationals,” the interior ministry said in a statement.

On Saturday, Putin addressed the tragic incident in a televised speech and vowed to punish those responsible.

The Russian President described those involved in the attack as “criminals (who) were cold-blooded and purposefully going to kill, shoot our citizens and our children at point-blank range”.

“They tried to hide and moved towards Ukraine, where, according to preliminary data, a window was prepared for them from the Ukrainian side to cross the state border,” he said.

“Whoever they are, whoever is guiding them. I repeat: we will identify and punish everyone who stands behind the terrorists.

“The main thing now is to prevent those who are behind this bloodbath from committing a new crime.”

Russia’s Investigative Committee, which probes major crimes, said on Saturday night AEDT the number of people killed in the attack had risen to 133 after initial reports stated 40 people were killed.

Russian investigators say the attackers also set fire to the concert hall using a “flammable liquid”.

It is expected the death toll will continue to rise.

Islamic State has claimed responsibility for the attack.

Russia is expected to respond with “extreme violence,” according to Matthew Sussex, a Russia expert and associate professor at the Australian National University.

Speaking to BBC News, Professor Sussex cited the aftermath of the 2002 Moscow theatre siege and 2004 Beslan school siege as examples.

“Perhaps it’s not so important who carried out the attacks but who the Russian government decides is to blame and who they are going to respond against,” he said.

50 victims identified

More than 145 people were wounded in the attack, some of them grievously.

Russia’s Health Minister Mikhail Murashko initially said 115 people were in hospital, including five children, with 60 of the victims in a serious condition.

So far, 50 of 133 people killed in the attack have been identified, NBC News reports.

According to The New York Times, most of the victims identified so far appear to be in their 40s.

Those killed include married couple Irina Okisheva and Pavel Okishev.

According to the Komsomolskaya Pravda newspaper, Mr Okishev had received tickets to the concert as an early present ahead of his 35th birthday next week.

Anastasiya Volkova also lost both of her parents in the shooting.

Ms Volkova said she had missed a phone call from her mother around the time of the attack. But when she called back there was no response.

“I couldn’t answer the phone. I didn’t hear the call,” she told 5 TV, as per The New York Times.

More disturbing footage of five heavily armed gunmen in camouflage gear has also appeared online showing the attack at the Crocus City Hall, to the northwest of Moscow, where Russian pop group Picnic was preparing to play.

Some of the footage, which showed people being shot at point blank range, is too graphic to be published.

Reports state ISIS, through its Amaq news agency, released the graphic footage.

Reports suggest the men entered the concert hall at around 8pm Friday night local time (4am Saturday AEDT) and began shooting at around 6200 people believed to be inside.

It has been reported they gained access through both the main entrance and underground parking lot.

The gunmen also threw a grenade or incendiary bomb which started a large fire in the building, according to a journalist for the RIA Novosti news agency who was at the scene.

“People who were in the hall were led on the ground to protect themselves from the shooting for 15 or 20 minutes,” the RIA Novosti journalist was quoted as saying.

People started crawling out when it was safe, the journalist reported.

About 100 people escaped through the theatre basement while others were sheltering on the roof, the emergency services ministry said on its Telegram channel.

News agency Reuters is reporting that ISIS-K, a splinter group of Islamic State (ISIS) claimed responsibility for the attack on its Telegram channel.

The BBC reported that ISIS-K is the Islamic State affiliate in Khorasan – an old term for a region that includes parts of Iran, Turkmenistan and Afghanistan.

It added that ISIS-K, frequently criticises Russian President Vladimir Putin in its propaganda, and accused Russia of atrocities against Muslim people in military campaigns in Chechnya and Syria, as well as in the Soviet-era invasion of Afghanistan.

The report claiming responsibility has not been independently verified, but US officials have said there is no reason to doubt it.

CBS is reporting that US official have confirmed that there has been a steady stream of information – dating back to November – about ISIS wanting to strike in Russia.

On 7 March, the FSB said it prevented an attack on a synagogue in Moscow that was being planned by an ISIS cell.

Accounts from the attack of witnesses who managed to escape are being reported by Russian media.

One witness, Vitaly, said he was in the concert hall on one of the balcony levels.

“We heard shots, we didn’t know what happened at first. Then I saw some terrorists shooting people,” he said.

“They threw some petrol bombs, everything started burning. We were led out towards an exit. The exit door was locked so we went to the basement of the venue, where we waited for rescuers.”

Another witness said there was a “terrible crush” as people tried to escape and people “were climbing on their heads to get out”.

An further unnamed witness said the venue was also hosting a children’s ballroom dancing competition at the time of the attack.

“Children and teenagers were at the competition. People came and said there was shooting.

A crush ensued. The children were running out in their ballroom gowns.”

Horrific footage posted online shows several men striding across the foyer outside the hall opening fire at members of the public, before rearming themselves, entering the hall and opening fire from a seating area.

Videos also show plumes of black smoke rising over the building. Russian media reported that the venue’s roof was collapsing.

Just over two weeks ago, the US embassy in Moscow issued a security alert after receiving reports that “extremists have imminent plans to target large gatherings in Moscow, to include concerts”.

At the time, US citizens were advised “to avoid large gatherings over the next 48 hours”.

Authorities have cancelled all public events in Moscow for the rest of the weekend and said a “terrorist” investigation had been launched.

President Vladimir Putin is receiving “constant” updates on the attack, his spokesman Dmitry Peskov told Russian news agencies.

Moscow mayor Sergei Sobyanin was the first to confirm that there were deaths in what he called a “terrible tragedy”.

“I offer my condolences to the families of the dead,” he said.

US authorities have said there is “no indication at this time” that Ukraine is involved in the attack.

– with AFP