Sky News has analysed IS footage of the attack and an image released by the militant group and spoken to experts about what the materials reveal.

Aaron Zelin, an expert on jihadist groups and senior fellow at the Washington Institute for Near East Policy, said "the attack itself, the type of people involved, the style of the attack and the media campaign" is all "Islamic State modus operandi".

IS has said it carried out the shooting massacre, and US officials have said their intelligence indicates that an Afghan affiliate, Islamic State Khorasan, or IS-K, was responsible. However, Vladimir Putin has not publicly mentioned IS in connection with the assailants.

The video

A day after the attack, IS released a video of the assailants inside Crocus Hall via the militant group's Amaq news agency which shows a number of gunmen storming the building and attacking people.

The attackers are seen holding guns and also knives. More than 130 people were killed and over 180 others were injured on Friday night.

Mr Zelin said the type of weapons used in the attack are consistent with IS methods. "We've seen in past attacks they shoot people and stab people... They have as many weapons on them as possible so they can inflict as much damage on them as possible.

"So, if they end up using all their bullets and cartridges or AK-47s they will still have a knife to stab."

While IS has also used other methods in previous attacks, including suicide attacks, another expert said that it would likely be easier to "procure firearms in Russia".

Dr Antonio Giustozzi, a senior research fellow at the Royal United Services Institute, said the way IS carries out attacks "depends on the kind of weapons they can obtain".

"So explosives, especially plastic explosives that you can use for suicide belts is not so easy to procure.... It's probably easier to procure firearms in Russia." He added the "exact choice of weapons can be dictated by what's available on the black market".

Clothing worn by suspects match IS image

IS also released an earlier image which they say shows some of the people behind the Moscow attack. It shows four people with blurred faces in front of an IS flag.

Mr Zelin said images "pledging allegiance to the leader of IS" are part of the group's media campaign.

Sky News has analysed and compared the IS image to subsequent interrogation videos and images by Russian authorities and other photos later taken of the four suspects in court. We used a facial recognition tool and analysed the clothing worn by the suspects.

Clothing worn by three of the people seen in the IS image matches those seen in other videos and images appearing in the aftermath of the attack.

We brightened the IS image above and matched details on the T-shirts worn by three of the people - to other images and videos on Telegram showing them being interrogated by Russian authorities.

The detailing of a logo on a T-shirt worn by one of the suspects in the image below appears blurred in the IS image (left), visible from a screenshot of the IS video (centre) and again on the T-shirt in an aftermath video (right).

The suspects have been named as Dalerdzhon Mirzoyev, Saidakrami Murodali Rachabalizoda, Muhammadsobir Fayzov and Shamsidin Fariduni.

We cross referenced the aftermath imagery and videos to photos of the four suspects pictured in court using an AI facial recognition tool which confirmed they matched.

Mr Zelin said that while not all IS attacks are the same, there is a consistency to the group's media campaign.

He explained they often include a line to first claim responsibility, followed by a longer statement, then "photographic evidence of the individuals pledging allegiance to the leader of IS", followed by some form of video of the attack or to do with the attack.

"It's definitely a template they use, part of it is to keep them in the news for a longer time," he added.

Claiming responsibility for attack

Experts are convinced no other group is responsible.

Dr Giustozzi said: "This is about, intimidating, spreading terror and primarily the recruitment and funding for the militant group."

Mr Zelin said in the aftermath of attack, he had seen in their "different types of propaganda in a number of different languages that they are trying to recruit people".

Russia's president Vladimir Putin has not publicly mentioned Islamic State in connection with the assailants, who he said had been trying to flee to Ukraine with help from "the Ukrainian side".

Ukraine has denied any role and Volodymyr Zelenskyy has accused Putin of seeking to divert blame.

Washington said it had warned Russia this month of an imminent attack. A source familiar with this intelligence said it was based on interceptions of "chatter" among IS-K militants.