Russian President Vladimir Putin has vowed to punish those responsible for the terror attack on a suburban Moscow concert hall that killed at least 133 people and according to Russian officials left about 145 more wounded.

It was one of the worst acts of terror in Russia in decades.

Throughout Russia tonight security has been beefed up.

And in Moscow people are remembering the dead and offering help to the wounded.

JOHN YANG (voice-over): Hundreds of people lined up in the rain this morning in Moscow to donate blood and plasma giving what they can for the wounded from last night's carnage.

YEKATERINA, Blood Donor (through translator): Of course I was shocked and filled with fear and horror.

I've been to a concert Crocus myself and when I saw those horrible videos, I was shocked and in tears even now when I speak about it, it was very scary to see at all.

JOHN YANG (voice-over): A branch of the Islamic State based in Afghanistan claimed responsibility for the attack began with gunmen storming the hall firing point blank at people who had gathered for a rock concert.

Dave Primov prima was among the crowd.

DAVE PRIMOV, Concert Attack Survivor (through translator): The shots were not sporadic.

They were constant volleys of gunfire.

We all got up and tried to move closer to the aisles.

People began to panic started to run and collided with each other some fell down and others trampled on them.

JOHN YANG (voice-over): Witnesses said the attackers through explosive devices that started a fire.

This morning a smoldering ruin was all that was left after the roof collapsed.

Investigators combed through wreckage looking for bodies and evidence.

In an address to the nation Russian President Vladimir Putin said all the gunmen had been arrested.

He never mentioned the ISIS claim of responsibility instead linking Ukraine to the attack.

VLADIMIR PUTIN, Russian President (through translator): Now the main thing is to not let those behind this bloodbath commit new crimes.

All four of the actual performers of the act of terror.

All those who shot and killed people were found and detained.

They tried to hide and we're moving in the direction of Ukraine.

There, according to preliminary data, they had a crossing of the border prepared from the Ukrainian side.

JOHN YANG (voice-over): Putin provided no evidence to support his claim and Kyiv denied any involvement.

U.S. Intelligence said they had warned Russian officials of a planned ISIS attack in Moscow.

Outside the ruins of the concert hall today, people left flowers at a makeshift memorial among them concert door Anastasia Rodionova who says she feels lucky to be alive.

ANASTASIA RODIONOVA, Concert Attack Survivor (through translator): They were just walking and shooting as they went along, gunning down everyone methodically in silence.

You understand only now that you are lucky, really lucky.

I came home my coat was just covered in blood.

Apparently someone shielded me.

JOHN YANG: Putin declared tomorrow a national day of mourning as the search goes on for answers about the brutal attack.

journalist Michael Weiss is the editor of The Insider and independent news outlet hovering Russia he's also co-author of "ISIS: Inside the Army of Terror."

Michael, what do we know about ISIS-K, this branch of ISIS that's claimed responsibility?

MICHAEL WEISS, Editor, The Insider: So ISIS-K is established in Afghanistan.

And they arranged against a host of other jihadi actors, including the Taliban, al Qaeda.

And they've been angling to hit Russia for quite a while.

If you look at their communication and their propaganda, they revile Vladimir Putin, one of the reasons being that Russia maintains a partnership with the Taliban, their sworn enemy.

The United States has fairly good intelligence on their capability and their motivation, because we occupied Afghanistan for more than 20 years.

And clearly, our departure has not really interfered with the ability to collect signals intelligence, which is what I believe the United States passed along to Moscow.

A little less than a month ago, on March 7, you'll recall the U.S. Embassy put out a notice advising people to stay away from public events for the next 48 hours.

And that indeed, according to reporting was tied to a credible ISIS-K threat planned for Russia.

JOHN YANG: And according also - - according to reporting, they also passed along that information to the Russians.

Why did Russian security miss this?

MICHAEL WEISS: Well, we don't know that they did.

I mean, it's always possible that some guys can slip through or that the intelligence was not specific enough to identify the time place and the kind of culprits that would be behind it.

But look, I mean, it's no mystery that Russia's security and military resources are predominantly poured into the war of conquest in Ukraine and also at the domestic level.

There's a lot a -- huge crackdown on dissent.

people arrested at Alexei Navalny's funeral a few weeks ago.

They're cracking down on any kind of anti-war demonstrations or protests, you know, if you so much is posted a news article from the New York Times about Russian casualties in Ukraine, you could be thrown in jail for several years.

So what we're seeing emerge in Russia is a kind of Neo-totalitarian state.

And under those conditions, the idea that, you know, the perfidious Americans are claiming that ISIS-K or some Islamist group is trying to attack Russia.

You can imagine the paranoia at the level of the Kremlin that they probably wouldn't credit that as plausible they would see it as some kind of psychological operation.

And I mean, indeed, President Putin came out today and sort of pointed the finger at Ukraine, even though it is highly implausible that Ukraine had anything to do with this whatsoever.

JOHN YANG: It not only pointed the finger in Ukraine, he didn't mention the ISIS claim of responsibility at all.

What do you think is going on with that?

MICHAEL WEISS: Well, it's embarrassing to Putin, right?

I mean, you know, the kind of light motif of his reign, at least in the first decade and a half was to reconstitute fortress, Russia, to make Russia this kind of impenetrable security state, which had all but withered away with the collapse of the Soviet Union.

You know, Putin himself, famously, former lieutenant colonel in the KGB, the KGB was colloquially known as the sword in the shield, right, it was there to protect the state and the sanctity of the state.

So for him, he's got a lot of egg on his face right now, because this wasn't just a kind of a terror attack where, you know, some lone wolf drove a car into a crowd.

This was highly sophisticated.

This had been planned for months, if you take ISIS at their word.

The Russian security services claimed to have detained four of the assailants.

And this was a machine gunfire into a crowded mall and concert venue, but also a fire set to burn the whole place down which it looks very much like they succeeded in that respect.

And now we're talking about over 100 people dead and many more wounded.

So this is going to be a trauma in Russia.

And so Putin, I think, is, as this is want is trying to deflect blame away from himself to point the finger at, you know, mysterious dark forces that are arrayed against Russia.

The question is, are the Russia people going to buy at this time?

JOHN YANG: What would you expect Putin to use this as sort of as a pretense in the in the war with Ukraine?

MICHAEL WEISS: Well, that's one of the fears.

Yeah.

I mean, if he's saying that, you know, the long dark arm of the Ukrainian intelligence services, and of course behind them, keep in mind, he always blames the United States, he thinks of Ukraine as a vassal not with no agency or sovereignty of its own.

But if he's pointing the finger at Ukraine, suggesting that, you know, these jihadists were making their way for the Russian-Ukrainian border, not a very clever exit strategy for anybody who's just carried out an attack like that, by the way.

One could then hypothesize he's using that as a pretext to escalate.

Now, you know, Russia has begun to refer to this operation in Ukraine, which is a war, as a war.

It's no longer just a special military operation.

There's been all kinds of rumors and reporting in the Russian press about a possible mobilization campaign, meaning a huge call up not a partial mobilization before, possibly another attempted attack to conquer Kharkiv in northeast Ukraine, a city that had been one of the main targets in February of 2022.

So we don't know.

And as you can imagine, because of this, it's led to any number of conspiracy theories.

I've seen many Ukrainians suggest that the Russians themselves may plan this as a false flag attack akin to the Moscow apartment bombings, Ukrainian military intelligence suggested as much.

In this case, I have to be honest, I mean, you know, I've spent a long time studying ISIS and their tactics and their motives and it certainly seems to me like what you see is what you get here.

ISIS-K looking to attack Russia, and succeeding in a spectacular fashion.

JOHN YANG: Michael Weiss, editor of The Insider, thank you very much.

MICHAEL WEISS: Sure, anytime.