All four suspects arrested after at least 133 killed in Moscow concert attack

AT least 133 people were killed and more than 140 injured when gunmen attacked a packed concert venue on the outskirts of Moscow, Russia says, reports the BBC.

A large fire engulfed the roof of the complex and dramatic video shows panicked concertgoers taking cover as shots and explosions ring out.

Russian President Vladimir Putin says all four gunmen have been arrested, and that the suspects were trying to flee to Ukraine - Kyiv says allegations of Ukrainian involvement are "absurd".

Putin calls the attack a "barbaric terrorist act" and announces a day of national mourning for 24 March.

Muscovites are queuing to give blood for those injured and flower tributes have been placed at the scene of the attack.

The US says it's credible that the Islamic State group could be behind the attack after the group said it did it. Russia has not commented.

People initially thought they heard firecrackers, says attack eyewitness

We've been hearing from some of the people caught up in last night's deadly attack on Moscow's Crocus Concert Hall.

One woman was with her 11-year-old daughter, buying ice cream at a café near the entrance, when they heard the noise and someone shouted to get down on the floor.

"We rushed to the children, lay down and started setting up barricades from tables and chairs, and several wounded people came running to us," a woman who was at the café with her 11-year-old daughter, has told BBC Russian.

Inside the theatre, the concert had been due to start in just a few minutes and some thought the noise might be part of the act.

Sofiko Kvirikashvili heard what she initially thought was "some kind of endless burst of firecrackers - I turned around in the hall once, then again. The third time, I realised everyone in the hall had started running away in all directions."

Dave Primov, the photographer, said there was a crush and a scene of panic. Some in the theatre tried to lie down between the seats, but with several gunmen opening fire in the stalls, that offered little protection.

Those in the audience who could, headed for the stage. Others tried to find higher exits, only to find some of the doors locked. Eyewitnesses said there were elderly people as well as children there, all caught up in the attack.