Vladimir Putin Says Moscow Concert Hall Shooting Death Toll at 133

The death count in Friday's tragic Moscow mass shooting is much higher than originally believed ... according to Russia's President Vladimir Putin.

The controversial head of state reportedly told the nation during a televised address that 133 people had been killed in the vicious attack at Crocus City Hall, a concert venue on Moscow's Western outskirts.

Putin likens the shooters to Nazis ... saying they killed in an organized fashion, aiming for Russian citizens and even children.

ISIS has claimed responsibility for the attack, but President Putin laid the blame squarely at the feet of Ukrainian officials ... saying they were working to let the perpetrators cross the border into their country.

FWIW ... an anonymous United States official told The Washington Post there's no reason to doubt the Islamic State's claim.

As we reported ... videos from the tragic shooting went viral -- showing graphic scenes of death and destruction at the music hall. People huddled behind chairs while gunshots echoed around the structure, and initial estimates put the death count at above 40.

Explosives were reportedly used during the attack, resulting in the whole building catching fire.

Officials in Western countries warned their citizens about venturing out to large public gatherings this month in the aftermath of Putin's recent election victory ... warning of possible terror attacks.

At least one man was detained by police last night ... caught on video being frisked with his hands up against a wall. It's unclear how many people were detained or how many were involved in the mass shooting.